INTERNAL DISEASES 401 



buted by Metchnikoff mainly to the leucocytes, which in all 

 human and animal bodies act as sentinels and destroy any 

 harmful matter which invades them. Buchner talks of alex- 

 ines, and many other writers of various specific " anti-bodies ". 

 All, however, agree that there are two sorts of immunity, (i) an 

 active immunity acquired after passing through an attack of the 

 disease, and (2) a passive immunity gained by the transference 

 of the active and acquired protective substance to a second and 

 previously healthy body, in order to guard it against some 

 definite disease. Obviously, hereditary immunity can only be 

 passive ; according to Ehrlich the transmission of the protec- 

 tive substance does not take place either in the ovum or sper- 

 matozoon, but only by means of the placenta and the milk of 

 the mother. He does not consider that either of these methods 

 of transmission clearly indicate a definitely hereditary immunity. 

 As, however, the question of acquired immunity is not finally 

 settled, Grober thinks it probable that certain variations are 

 present in the germ cells which lead to the development of 

 special powers or tendencies. 



($) Non- Infectious Diseases. 



Diseases due to animal parasites naturally come next to the 

 infectious, for parasitic animals maintain their existence at the 

 expense of the human organism, and partially secrete poisonous 

 substances, such as occur in the infectious diseases. The differ- 

 ence is that the parasite produces local more than general disease. 



Internal Parasites. Of parasitic nematodes only the follow- 

 ing are peculiar to man : 



Oxyuris vermicularis (Plate VI., fig. i) ; Trichocephalus 

 dispar (Plate VI., fig. 2) ; the rare Filaria labialis of Pane (Plate 

 VI., fig. 3); and the Filaria bronchialis (Plate VI., fig. 4); the 

 Filaria loa of Guyot, which lives beneath the conjunctiva of the 

 negroes on the Congo and Gabon ; the Filaria lentis of Dies, 

 which is sometimes found in lenses after removal (Plate VI., 

 fig. 5) ; the Filaria sanguinis hominis, found in its embryonic 

 condition in large numbers in the blood of man in the tropics 

 of both the Old and New World (Plate VI., fig. 6), and two 

 tiny varieties of Anquillula (A. stercoralis and A. intestinalis) 

 found respectively in Cochin China and Italy. 



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