1C2 



PHYSIOLOGY 



and lastly, the essential constituent of tin 4 i'< - ll is 

 dis.-overcd in Protoplasm (ij.v. |. The last three 

 stages, beginning with th' anal .VMM of organs into 

 tissues, have IM-I-II developed witiiin tin 4 last liiiiulreil 

 vein-. Tin 4 history looked at from this |>iiit of 

 view is enlarged upon in the article l.nn.oGY; 

 hen- \M' shall give a history of a n.ore ili'laile<l 

 iiatiuc. Preycr divides it into five periods (1) 

 the s|>ecnlative |>eriod ; (2) that associated with 

 the name of \ti-ii.ile; (3) headed hy tialen, 

 (41 liy Harvey ami Ilaller, and ( "> ) hy Mullet. 

 The first period opens with the beginning of medi- 

 ral science in India, China, and Egypt. The .lews 

 were aei|ii:iinted with many laws of practical 

 hygiene and dietetics. Then came the phiraMphen 

 of (Jreece. Matter was supposed to consist of four 

 element-, lire, air, earth, and water. The essence 



of life was referred lir-t t le and then to another 



of these elements by various philosophers : hy Thales 

 to water, hy . \naximencs to the air, hy Xenophon 

 to the earth, hy Pythagoras to lire or heat. Hip|n>. 

 crates, the fatlici of medicine, ahont 4.~>0 B.C., was 

 the first to proceed in a purely rational spirit. 

 Observing carefully the facts of disease, he strove 

 to found the art of medicine upon the results of 

 experience. He attrihnted diseases to natural 

 causes, ami not to special visitations of the gods ; 

 and as already noted, he postulated a spiritual 

 essence universally diffused ; this he called Nature, 

 Physis, and to this he ascribed the maintenance of 

 things in their normal state, and their restoration 

 if disturbed. The second period is headed hy Aris- 

 totle. the father of natural history, about 850 B.C. 

 He disserted many animals, and attempted to dis 

 cover the uses of the various parts. It is difficult to 

 est imate correct ly the exact value of Aristotle's work 

 in physiology; it must he measured more hy the 

 methods of n-->-;u'-h which he initiated than hy the 

 actual results achieveil. Thus, to give an example 

 of his ideas on the subject, the heart he imagined 

 as the seat of the 4 rational soul ; ' the nerves he sup- 

 jMised to arise in the heart ; of their function he w as 

 ignorant. What in perha|>s more surprising is that 

 he deserilM'd the hrain its an inert viseus, cold and 

 hloodlcss, whose only function was to cool the 

 heart, and not comparahle in importance to the 

 other organs of the body. Erasislratus. the grand- 

 son of Arisloih-, ahout H<K) II. c. . was perhaps I he first 

 to carefully dissect the human hrain. He traced 

 tin 1 connection of nerves with it, and even noticed 

 that the complexity of the convolutions of the gray 

 matter was greatest in man, and that they were 

 to some extent a measure of the intelligence. The 

 next 400 veais were harren of any useful advance; 

 the practice of medicine reached perhaps its lowest 

 |M)int. The literature is occupied with discussions 

 ax to the 'animal ami vital spirit-,' terms used 

 Itefore Aristotle to express the powers of living 

 things. The animal spirits were those that ruled 

 ivcr those art inn* of living things that were sup 

 posed to he <|iiit* different from anything that lakes 

 place in things not living, while the vital spirits 

 were those that were concerned in those processes 

 going on in the body which were the result of 

 purely chemical and physical laws. We no longer 

 discuss whether the vital spirits live in the In-art 

 and the animal in the hrain. 'hut we have not 

 yet settled the exact relationship between the pro 

 ceiwe* of the living world and those of inorganic 

 matter. 



Alton! l.TO A.I). <Jalen, a Unman, revived the 

 sounder method of experimental ini|uiry ; he is the 

 leader of the third period. He perceived that mere 

 dis-ertion of dead animals gives no infallihle infor- 

 mation us to the functions of the living, and accord 

 ingly |M 4 rformed many experiments u|>n living 

 animal-. He proved that during life the arteries 

 contain hlood and not air, as was thought to he 



the case up to that time, hy simply opening a 

 vessel of a living animal. He also directed much 

 of his study to the hrain and nervous system, lie 

 was the lirst to state definitely that the hrain, 

 spinal cord, ami nerves are the oigans of sensa- 

 tion, intelligence, and the originators and guides 

 of pro|H-rly ordered voluntary movements : and he 

 finally refuted the doctrine of Aristotle hy showing 

 that the hrain was hot and not cold, and hy arguing 



also that if it were a mere i ler of the hlood it need 



not lie elaborately organised. He pointed out that 

 the hrain w.-us of the same suhsiaiice as ihe nerve-. 

 hut softer, 'as it should necessarily he. inasmuch 

 as il receives all the sensations, perceives all the 

 imaginations, and then has to comprehend all the 

 ohjccts of the understanding, for what i- soft is 

 more easily changed that what is hard.' He dis- 

 covered also thai the nerves .,t -en-ation and of 

 motion an- distinct, and thus explained the douhle 

 supply of nerves to the tongue and eyes. For cen- 

 turies tlalcn exeiriscd an undisputed sway over the 

 practitioners of medicine and the students of allied 

 philosophy. 



Some centuries afterwards the so called Arahhin 

 physiology aio-e. Avicenna, aliout the year I IK 10, 

 was its chief exponent. (Mice more, however, t lied is 

 (Missions were atiout the nature ami residence of the 

 animal and vital spirits. Alhertus Magnus, in the 

 13th century, and Paracelsus, in the l.'ith century, 

 are representatives of media-vat mysticism. Aliout 

 the same time, during the revival of learning, the 

 mathematicians and chemists were Imsx seeking to 

 explain bodily functions in terms of mechanical, 

 chemical, and physical laws. In the 16th century 

 Yillaiiovaiius described correctly the action of tin- 

 lungs as purifiers of the venous hlood. The study of 

 human anatomy was revived hy Vesalius in Italy, 

 and continued hy Kahricius ; and in the beginning 

 of the 17th century Harvey, who had studied in 

 Italy, made perhaps the most important of all 

 physiological discoveries, that of the circulation of 

 the hlood. 



This discovery inaugurates the fourth period of 

 the history of physiological research ; hy il a sound 

 foundation for the- whole science was laid, and the 

 development of surgery and medicine made possihle. 

 Then, after the invention of the microscope, came 

 many active investigators; among them may he 

 mentioned Malpighi and l.ceuwcnhoek ; and thus 

 tin- foundations of Histology (i|.v.) wen- laid. 

 Ilaller. near the end of the ISth century, gave to 

 physiology the form that it now po--c--e-. ||,. 

 attempted to discard from tin- science all stale 

 menls of a vague and m\stical character, he added 

 many minor discoveries to the store of facts, and 

 rund the whole in a logical sequence. 



The great leader of the fifth period, .Johannes 

 Midler, during the first half of Ihe lilth crntury, 

 gave to the science a greater width. He connected 

 as one philosophy tin- truths of chemical physics, 

 comparative anatomy and physiology, and embry- 

 ology. Embryology was founded as a science hy 

 Yon liaer. Cuvier developed com pal alive anatomy, 

 ami thus gave a foundation to the study of co'm 

 punitive physiology. Lamarck enunciated the laws 

 of evolution. Itcrzelius placed animal chemistry 

 U|MIII a sound hasis. The discovery of the mechani- 

 cal e>|iiiv alent of heat hy .louh-. ti nunciation of 



tJn- cell-theory hy Schlciden and Schwaiin. and tin- 

 discovery of protoplasm as the essential const ituent 

 of the cells hy Yon Mold and I >u . I aid in are 1 lie great 

 -t"p- which have placed u- in our present position. 

 Tin- discovery of reflex action hy Mai-shall Hall, 

 of inhibitory nerve action by Welx-r, and of the 

 glycogenic function of the liver by Claude liernard 

 mark important advances. With the work of this 

 la-t mentioned the physiology of Protoplasm (o,.v.) 

 Ix-gins. The conception of evolution, rendered 



