368 PHYSIOLOGY CHAP. 



biological sciences. If we grant the doctrine of evolution, the 

 question is implicitly answered in the sense that man as we know 

 him to-day is descended from a lower form and has gradually 

 developed, passing through various intermediate stages, until he 

 reached his present form. What the causes and conditions were 

 which determined, promoted, and facilitated this evolution, whether 

 they were external or internal, is still under discussion. (See 

 Chap. II., Vol. I.) 



The animal form, which from the morphological point of view 

 most closely resembles man as we know him to-day, is that of the 

 monkey, as was recognised by Linnaeus, who placed man and the 

 ape in the same class of the highest order of animals. Later 

 researches have shown that all monkeys are not equally like man ; 

 the relationship is only strongly marked in the gibbon, the 

 orang-outang, the gorilla, and the chimpanzee, which were there- 

 fore placed in a special class that of the so-called anthropoid or 

 anthropomorphous monkeys. The latest researches have proved 

 this relationship still more plainly. 



Whatever system of organs we select, we shall always find a 

 great morphological resemblance between man and this group, so 

 much so as to prove the truth of Huxley's assertion that the gap 

 between anthropoids and man is relatively smaller than that 

 between anthropoids and other monkeys. 



The direction of the cavities of the eyes, which are separated 

 by a bony septum, the characteristic shape of the pinna of the 

 ear, the hairless palms and soles, the position and direction of the 

 primitive piliferous system, and more especially the first stages of 

 foetal development, are the same in man and anthropoid. Recent 

 physiological, chemico-physiological, and pathological researches 

 have shown this relationship to be even closer. Thus Friedental 

 found that the blood of the anthropoid is the only kind which can 

 be transfused into the blood-vessels of man without having the 

 toxic effects which we have already seen (Chap. V., Vol. I.) to result 

 from the transfusion of heterogeneous blood ; this proves the blood 

 of anthropoids and man to be homogeneous. 



If we have recourse to the so-called reaction to serum, first 

 proposed by Uhlenhuth, we arrive at the same conclusion. This 

 reaction consists in giving on successive days some animal (rabbits 

 are generally used) hypodermic injections of small quantities of 

 the blood of other animals, which provoke in the animal experi- 

 mented on, a reaction, the formation or increase of special proteid 

 substances in the plasma of _ the blood, which precipitate certain 

 proteid substances in the serum of the blood of the animal supply- 

 ing the blood. This reaction takes place readily in a test-tube, 

 even if only extremely small quantities of the two sera are used, 

 and is specific for both animals. It has now been found that 

 rabbits treated with an injection of human blood produce a serum 



