PHYSIOLOGY. 



C69 



eluding under tho term medium all physical 

 forces falling upon them, as well as matters 

 bathing them ; and we may conclude that from 

 the primary characters thus produced there 

 must result secondary characters. When the 

 respective effects of gravitation, heat, light, 

 etc., are studied, as well as the respective ef- 

 fects, physical and chemical, of the matters 

 forming the media, water and air, it will be 

 found that while more or less operative on all 

 bodies, each modifies organic bodies to an 

 extent immensely greater than the extent to 

 which it modifies inorganic bodies'. The most 

 general trait of such effects is the greater 

 amount of change wrought by them on the 

 outer surface than in the inner mass of the 

 bodies affected. The matters composing the 

 medium must act more on the parts directly 

 exposed to them than on the parts sheltered 

 from them; and the forces pervading it, ex- 

 cept gravity, which affects outer and inner 

 parts indiscriminately, must exert the larger 

 share of their actions upon the outer parts. 

 Hence, the primary and almost universal effect 

 of the converse between the body and its me- 

 dium is to differentiate its outside from its in- 

 side. This differentiation is exemplified and 

 exhibited in all cell- organisms, beginning with 

 the unicellular, in the cell-envelope, which is 

 an outside, differentiated by the influence of 

 the environment from the cell-content. The 

 operation of this same force producing this ef- 

 fect in primary organisms has predetermined 

 the universal cell-structure of all embryos, 

 plant and animal, and the consequent celi-com- 

 position of adult forms arising from them. 

 The differentiation of outer from inner reap- 

 pears in the aggregations of cell-units which 

 constitute living organisms. In its simplest 

 and most unmistakable form we see this in the 

 early changes of an unfolding ovum of primi- 

 tive type. The original fertilized single cell 

 having multiplied into a cluster of cells, then 

 begins to show itself a contrast between pe- 

 riphery and center ; and presently there is 

 formed a sphere consisting of a superficial layer 

 unlike its contents. In another class of organ- 

 isms as in leaves from the thallus of a sea- 

 weed up to the leaf of a highly developed 

 phaBnogam, we find, at all stages, a contrast 

 between the inner and outer parts of these 

 masses of flattened tissue. Then, in the out- 

 sides of the leaves a differentiation appears de- 

 pendent on exposure to the light. In the 

 frond of Marchantia potymorpha the side 

 which happens to fall uppermost and is exposed 

 to the light, forms stomata, while the under 

 and dark side produces root-hairs and leafy 

 processes. In roots, while in darkness and sur- 

 rounded by moist earth, the protective coats 

 are comparatively thin; but when the acci- 

 dents of growth entail permanent exposure to 

 light and air, roots acquire coverings allied in 

 character to the coverings of branches. Similar 

 modifications of the integument by the environ- 

 ment are seen in men in the hardening and 



roughening of the skin by exposure and usage, 

 and the healing of wounds. So in all animal 

 life, the outer surface, with the in-foldings and 

 ingrowings to which it conforms, is the part 

 which is modified by contact with the environ- 

 ment, and in which are initiated the various 

 instrumentalities for carrying on intercourse 

 with it. Clearly, organization could not but 

 begin on the surface; and, having thus begun, 

 its subsequent course could not but be deter- 

 mined by its superficial origin. Doubtless, 

 natural selection soon came into action, but it 

 could operate only under subjection; it could 

 do no more than take advantage of those struct- 

 ural changes which the medium and its con- 

 tents had initiated. Thus this primordial fac- 

 tor of the influence of the environment by 

 causing the first differentiations of those clus- 

 ters of units out of which visiUe animals in 

 general arose, fixed the starting-place for or- 

 ganization, and therefore determined the course 

 of organization ; and doing this, gave indelible 

 traits to embryonic transformations and to 

 adult structures. 



Prof. Kudolf Virchow defines acclimatiza- 

 tion by saying that when a person goes to a 

 different climate from that to which he has 

 been accustomed, he feels at first uncomforta- 

 ble, but after some weeks finds his system re- 

 gaining its equilibrium. He has then accom- 

 modated himself to the new conditions; his 

 organs have endured material change. Two 

 kinds of effects accompany the course of accli- 

 matization ; simple discomfort or climatic in- 

 disposition, and disease or climatic illness, 

 which differs from the former by possessing 

 the element of danger as distinguished from 

 simple inconvenience. Much has been pub- 

 lished by the French and English on the sub- 

 ject, yet researches are entirely wanting upon 

 the special changes which precede the onset of 

 disease. On the other hand, the clinical study 

 of tropical disease itself has been very much 

 advanced. Whoever studies acclimatization 

 must do so with a view to establish certain 

 geographical limits of ethnological provinces 

 analogous to botanical and zoological provinces. 

 Comparing the capability of the different 

 white races for acclimatization, the Semitic 

 race is found to be superior to the Aryan. 

 Among Aryan race?, those of the south (Portu- 

 guese, Spanish, and Maltese) are superior to 

 those of the north. Races, with a strong 

 Semitic admixture, are more easily acclimatized 

 than the pure Aryan stock. A population 

 transplanted into a distant country often re- 

 mains apparently stationary, though its new 

 latitude may not be greatly different from that 

 in which it flourished at home. It suffers 

 from a decrease of fecundity and an arrest of 

 development which may go to the end of the 

 complete elimination of its posterity. Such is 

 the case, among other instances, with the 

 British in India, whose life never exceeds throe 

 generations, and all attempts by sanitary meas- 

 ures to perpetuate it have failed. Medical 



