A History of Science, vol 4 - Henry Smith Williams (epub e ink reader .txt) 📗

is generally understood, is an enlargement

of a certain part of an artery, this enlargement sometimes

becoming of enormous size, full of palpitating blood, and likely

to rupture with fatal results at any time. If by any means the

blood can be allowed to remain quiet for even a few hours in this

aneurism it will form a clot, contract, and finally be absorbed

and disappear without any evil results. The problem of keeping

the blood quiet, with the heart continually driving it through

the vessel, is not a simple one, and in Hunter’s time was

considered so insurmountable that some surgeons advocated

amputation of any member having an aneurism, while others cut

down upon the tumor itself and attempted to tie off the artery

above and below. The first of these operations maimed the patient

for life, while the second was likely to prove fatal.

 

In pondering over what he had learned about collateral

circulation and the time required for it to become fully

established, Hunter conceived the idea that if the blood-supply

was cut off from above the aneurism, thus temporarily preventing

the ceaseless pulsations from the heart, this blood would

coagulate and form a clot before the collateral circulation could

become established or could affect it. The patient upon whom he

performed his now celebrated operation was afflicted with a

popliteal aneurism—that is, the aneurism was located on the

large popliteal artery just behind the knee-joint. Hunter,

therefore, tied off the femoral, or main supplying artery in the

thigh, a little distance above the aneurism. The operation was

entirely successful, and in six weeks’ time the patient was able

to leave the hospital, and with two sound limbs. Naturally the

simplicity and success of this operation aroused the attention of

Europe, and, alone, would have made the name of Hunter immortal

in the annals of surgery. The operation has ever since been

called the “Hunterian” operation for aneurism, but there is

reason to believe that Dominique Anel (born about 1679) performed

a somewhat similar operation several years earlier. It is

probable, however, that Hunter had never heard of this work of

Anel, and that his operation was the outcome of his own

independent reasoning from the facts he had learned about

collateral circulation. Furthermore, Hunter’s mode of operation

was a much better one than Anel’s, and, while Anel’s must claim

priority, the credit of making it widely known will always be

Hunter’s.

 

The great services of Hunter were recognized both at home and

abroad, and honors and positions of honor and responsibility were

given him. In 1776 he was appointed surgeon-extraordinary to the

king; in 1783 he was elected a member of the Royal Society of

Medicine and of the Royal Academy of Surgery at Paris; in 1786 he

became deputy surgeon-general of the army; and in 1790 he was

appointed surgeon-general and inspector-general of hospitals. All

these positions he filled with credit, and he was actively

engaged in his tireless pursuit of knowledge and in discharging

his many duties when in October, 1793, he was stricken while

addressing some colleagues, and fell dead in the arms of a

fellow-physician.

LAZZARO SPALLANZANI

Hunter’s great rival among contemporary physiologists was the

Italian Lazzaro Spallanzani (1729-1799), one of the most

picturesque figures in the history of science. He was not

educated either as a scientist or physician, devoting, himself at

first to philosophy and the languages, afterwards studying law,

and later taking orders. But he was a keen observer of nature and

of a questioning and investigating mind, so that he is remembered

now chiefly for his discoveries and investigations in the

biological sciences. One important demonstration was his

controversion of the theory of abiogenesis, or “spontaneous

generation,” as propounded by Needham and Buffon. At the time of

Needham’s experiments it had long been observed that when animal

or vegetable matter had lain in water for a little time—long

enough for it to begin to undergo decomposition—the water became

filled with microscopic creatures, the “infusoria animalculis.”

This would tend to show, either that the water or the animal or

vegetable substance contained the “germs” of these minute

organisms, or else that they were generated spontaneously. It was

known that boiling killed these animalcules, and Needham agreed,

therefore, that if he first heated the meat or vegetables, and

also the water containing them, and then placed them in

hermetically scaled jars—if he did this, and still the

animalcules made their appearance, it would be proof-positive

that they had been generated spontaneously. Accordingly be made

numerous experiments, always with the same results—that after a

few days the water was found to swarm with the microscopic

creatures. The thing seemed proven beyond question—providing, of

course, that there had been no slips in the experiments.

 

But Abbe Spallanzani thought that he detected such slips in

Needham’s experiment. The possibility of such slips might come

in several ways: the contents of the jar might not have been

boiled for a sufficient length of time to kill all the germs, or

the air might not have been excluded completely by the sealing

process. To cover both these contingencies, Spallanzani first

hermetically sealed the glass vessels and then boiled them for

three-quarters of an hour. Under these circumstances no

animalcules ever made their appearance—a conclusive

demonstration that rendered Needham’s grounds for his theory at

once untenable.[2]

 

Allied to these studies of spontaneous generation were

Spallanzani’s experiments and observations on the physiological

processes of generation among higher animals. He experimented

with frogs, tortoises, and dogs; and settled beyond question the

function of the ovum and spermatozoon. Unfortunately he

misinterpreted the part played by the spermatozoa in believing

that their surrounding fluid was equally active in the

fertilizing process, and it was not until some forty years later

(1824) that Dumas corrected this error.

THE CHEMICAL THEORY OF DIGESTION

Among the most interesting researches of Spallanzani were his

experiments to prove that digestion, as carried on in the

stomach, is a chemical process. In this he demonstrated, as Rene

Reaumur had attempted to demonstrate, that digestion could be

carried on outside the walls of the stomach as an ordinary

chemical reaction, using the gastric juice as the reagent for

performing the experiment. The question as to whether the stomach

acted as a grinding or triturating organ, rather than as a

receptacle for chemical action, had been settled by Reaumur and

was no longer a question of general dispute. Reaumur had

demonstrated conclusively that digestion would take place in the

stomach in the same manner and the same time if the substance to

be digested was protected from the peristalic movements of the

stomach and subjected to the action of the gastric juice only. He

did this by introducing the substances to be digested into the

stomach in tubes, and thus protected so that while the juices of

the stomach could act upon them freely they would not be affected

by any movements of the organ.

 

Following up these experiments, he attempted to show that

digestion could take place outside the body as well as in it, as

it certainly should if it were a purely chemical process. He

collected quantities of gastric juice, and placing it in suitable

vessels containing crushed grain or flesh, kept the mixture at

about the temperature of the body for several hours. After

repeated experiments of this kind, apparently conducted with

great care, Reaumur reached the conclusion that “the gastric

juice has no more effect out of the living body in dissolving or

digesting the food than water, mucilage, milk, or any other bland

fluid.”[3] Just why all of these experiments failed to

demonstrate a fact so simple does not appear; but to Spallanzani,

at least, they were by no means conclusive, and he proceeded to

elaborate upon the experiments of Reaumur. He made his

experiments in scaled tubes exposed to a certain degree of heat,

and showed conclusively that the chemical process does go on,

even when the food and gastric juice are removed from their

natural environment in the stomach. In this he was opposed by

many physiologists, among them John Hunter, but the truth of his

demonstrations could not be shaken, and in later years we find

Hunter himself completing Spallanzani’s experiments by his

studies of the post-mortem action of the gastric juice upon the

stomach walls.

 

That Spallanzani’s and Hunter’s theories of the action of the

gastric juice were not at once universally accepted is shown by

an essay written by a learned physician in 1834. In speaking of

some of Spallanzani’s demonstrations, he writes: “In some of the

experiments, in order to give the flesh or grains steeped in the

gastric juice the same temperature with the body, the phials were

introduced under the armpits. But this is not a fair mode of

ascertaining the effects of the gastric juice out of the body;

for the influence which life may be supposed to have on the

solution of the food would be secured in this case. The

affinities connected with life would extend to substances in

contact with any part of the system: substances placed under the

armpits are not placed at least in the same circumstances with

those unconnected with a living animal.” But just how this writer

reaches the conclusion that “the experiments of Reaumur and

Spallanzani give no evidence that the gastric juice has any

peculiar influence more than water or any other bland fluid in

digesting the food”[4] is difficult to understand.

 

The concluding touches were given to the new theory of digestion

by John Hunter, who, as we have seen, at first opposed

Spallanzani, but who finally became an ardent champion of the

chemical theory. Hunter now carried Spallanzani’s experiments

further and proved the action of the digestive fluids after

death. For many years anatomists had been puzzled by pathological

lesion of the stomach, found post mortem, when no symptoms of any

disorder of the stomach had been evinced during life. Hunter

rightly conceived that these lesions were caused by the action of

the gastric juice, which, while unable to act upon the living

tissue, continued its action chemically after death, thus

digesting the walls of the stomach in which it had been formed.

And, as usual with his observations, be turned this discovery to

practical use in accounting for certain phenomena of digestion.

The following account of the stomach being digested after death

was written by Hunter at the desire of Sir John Pringle, when he

was president of the Royal Society, and the circumstance which

led to this is as follows: “I was opening, in his presence, the

body of a patient of his own, where the stomach was in part

dissolved, which appeared to him very unaccountable, as there had

been no previous symptom that could have led him to suspect any

disease in the stomach. I took that opportunity of giving him my

ideas respecting it, and told him that I had long been making

experiments on digestion, and considered this as one of the facts

which proved a converting power in the gastric juice… . There

are a great many powers in nature which the living principle does

not enable the animal matter, with which it is combined, to

resist—viz., the mechanical and most of the strongest chemical

solvents. It renders it, however, capable of resisting the powers

of fermentation, digestion, and perhaps several others, which are

well known to act on the same matter when deprived of the living

principle and entirely to decompose it. “

 

Hunter concludes his paper with the following paragraph: “These

appearances throw considerable light on the principle of

digestion, and show that it is neither a mechanical power, nor

contractions of the stomach, nor heat, but something secreted in

the coats of the stomach, and thrown into its cavity, which there

animalizes the food or assimilates it to the nature of the blood.

The power of this juice is confined or limited