VEGETABLE AND ANIMAL ALBUMEN. 545 



taken. If to these facts tlie results of chemical investigations be 

 added, showing that many constituents of the greatest vital impor- 

 tance in both are identical, and that a close relationship of others 

 (vegetable and animal fats) is beyond doubt, we may justly claim that 

 chemistry has contributed and will further contribute considerable sup- 

 port to the doctrine of evolution, if identity of matter may be regard- 

 ed as evidence of consanguinity, or as a proof of common descent. 



Considered from another point of view the mutual relations exist- 

 ing between both classes of beings are of a decidedly hostile character. 

 The fierce " struggle for life," which causes animals to kill and to de- 

 vour their fellow-creatures, is in a not less merciless degree extended 

 to plants ; and victory is not, as we might fancy, always on the 

 side of the more perfect creature. Even man, the most accomplished 

 being, and at the same time the most relentless despot on the earth, 

 though without much personal trouble he may fell the strongest trees 

 and eradicate whole forests, is yet liable to succumb to the attacks 

 of a few micro-organisms invisible to the human eye. A theory, at 

 first pointed out by Pasteur, accepted by Virchow, and of late experi- 

 mentally confirmed by Metschnikoff, teaches, that certain low plants, 

 fungi, called microbia, or bactei'ia, said to be the primary causes of in- 

 fectious diseases, when entering the circulation of blood or one of the 

 important organs of the body, become at once engaged in a struggle 

 ■with the living cells of the organism, both adversaries endeavoring to 

 kill and to devour each other ; the result of this fight, if the microbia 

 are victorious, is said to be the death of the animal. 



In a lively and perspicuous representation Metschnikoff has de- 

 scribed one of these destructive combats. Dajj/mia, a sweet water 

 crustacean, served to him as the first object on which he could observe 

 the attack by monospora, a fungus of the lowest order. As soon as 

 the latter began to invade the body of Daphnia it became surrounded 

 and entangled by numerous cells {leucocytes) engaged in lively mo- 

 tion, which gradually from all sides attached themselves to the fungus 

 and destroyed it by some kind of intercellular digestion, or absorption. 

 It is evident, that a single cell could not afford to give out so much dis- 

 solving matter as was required for this purpose ; it would even proba- 

 bly have succumbed to the enterprising enemy ; but by the assistance 

 of its confedei'ates it succeeded in overwhelming the intruder. In 

 eighty cases out of a hundred, according to Metschnikoff, the cells 

 would be victorious, but in twenty cases the fungus would gain the 

 battle, with the consequent death of the Daphnia. 



Concerning this view and interpretation of the origin and progress 

 of infectious diseases, we are inclined to believe that, since bacteria 

 have not been found in all of them, and since, where they are present, 

 also certain products of chemical decomposition of proteids, ptomaines, 

 occur with them — the dangerous phenomena and the lethal end of such 

 diseases should rather be ascribed to the well-known virulent proper- 

 V01-. XXXII. — 35 



