INTERNAL DISEASES 399 



through the sting of the tsetse fly (Glossina palpalis) ; there it 

 undergoes a change and multiplies, setting up the fatal " sleeping 

 sickness ". In monkeys which have been secondarily infected 

 with the blood or cerebro-spinal fluid of these patients, the disease 

 takes the same course. Dogs and rats are only infected with 

 difficulty ; donkeys, oxen, goats, sheep and guinea-pigs have so 

 far appeared insusceptible. 



Another kind of tsetse fly (Gossina morsitans) stings horses 

 and cattle, infects them with the Trypanosoma Brucei, and thus 

 produces the dreaded Nagana, which has never been communi- 

 cated to man. It is analogous to the Surra of India and the 

 Mai de Caderas of South America. 



Since the bacillus icteroides described by Sanarelli in 1897 

 has ceased to be regarded as the cause of yellow fever, evidence 

 has accumulated to show that this disease is due to the sting of 

 a mosquito (Stegomya fasciata) whereby an incredibly small 

 protozoon is introduced into the body. The death of Walter 

 Meyers was attributed in England to his having been stung by 

 mosquitoes which had settled on yellow fever patients ; and more 

 recent researches have confirmed the correctness of this view. 

 Yellow fever has always been regarded as a disease only occur- 

 ring in man, but according to Friedberger and Frohner horses 

 and dogs are also attacked. 1 



At the close of this chapter on the infectious diseases, 

 malignant new growths, carcinoma and sarcoma may also be 

 mentioned, as a number of investigators in all countries (e.g.> 

 v. Leyden) take the view that they are caused by a parasitic 

 inoculation and by the growth of an infective agent. We can- 

 not here enter into the pros and cons of this view ; still less can 

 we describe the numerous cancer parasites discovered by various 

 investigators. For our present purpose it is enough to state that 

 dogs, horses, cattle, mice, and even salt-water fishes, are subject 

 to malignant new growths, as well as man ; that the tendency 

 towards it at any rate is hereditary, and that it is possible to 

 inoculate an animal with cancer, or to transplant it from one 

 animal to another of the same species. 



As we have seen, a large series of infectious diseases are 

 peculiar to man, and are only primarily seen in him, namely, 



1 Friedberger und Frohner, loc. cit., ii., p. 737. 



