340 



SCIENCE 



[N. S. Vol. XLIV. No. 1132 



Belapsing fever (Spirochceta ober- 

 meieri) . 

 Bed bugs: 



Kala azar. 

 Flies : 



Sandfly fever. 



Sleeping sickness (tse-tse fly). 

 Typhoid fever and other infections car- 

 ried mechanically. 

 Crustaceans (water flea) : 



Guinea worm infection (dracuncu- 

 losis). 

 Oysters, clams, etc.: 



Typhoid fever. 

 Snails : 



Trematode infections (especially bilhar- 

 ziosis) . 



In this outline I have included the most 

 important human diseases that in one way 

 or another are wholly or to some extent 

 dependent on lower animals for their exist- 

 ence and transmission. As given the list is 

 not entirely complete, and if it were com- 

 plete to-day it might not be complete to- 

 morrow, so rapidly are discoveries espe- 

 cially in tropical diseases being made. The 

 role that lower animals play in the trans- 

 mission of intestinal parasites, for example, 

 is exceedingly varied and though a prodigi- 

 ous number of these parasites have been 

 described and their hosts and intermediate 

 hosts determined there are still very many 

 about which little or nothing is known. In 

 the outline as given I have mentioned only 

 some of the more important examples in 

 this great group. 



I wish now to briefly analyze some of the 

 relations of the lower animals to human 

 disease transmission. We find these rela- 

 tions in certain instances to be very simple, 

 in other instances extremely varied and 

 complex. The direct portals of entry into 

 man are usually through the skin, the res- 

 piratory and the gastro-intestinal tracts. 

 In some diseases transmission can occur in 

 only one way. In others the transmission 

 may take place in a great variety of ways. 

 I will first group and summarize the modes 

 of transmission as follows: 



I. Infection in man may occur through 

 simple contact with diseased animals. Ex- 



cretions from lesions of skin, nose, lungs 

 and intestines are the usual vehicles. As 

 examples we may cite glanders, anthrax 

 and cowpox. Previous wounds of the body 

 surface may or in some cases may not be 

 necessary for the transmission. The virus 

 also may enter the body through the res- 

 piratory or gastro-intestinal tracts. "While 

 often this method of transmission is simple 

 and direct, at times the virus may be 

 carried long distances in very indirect and 

 circuitous routes from the animal to man. 

 This is particularly true of the spore-bear- 

 ing organisms. Recently an outbreak of 

 several cases of anthrax occurred in Eng- 

 land which after considerable difficulty was 

 traced to the use of infected shaving 

 brushes. The anthrax bacilli were re- 

 covered from the used brushes as well as 

 from new brushes from the same stock 

 obtained in a store. They were made with 

 hair from a diseased animal. 



II. The infectious agent may be carried 

 mechanically from person to person or 

 from animal to person through food or 

 otherwise by a second animal; as in the 

 transmission of typhoid, dysentery, cholera, 

 etc., by flies. Foot and mouth disease is 

 said to be carried over long distances by 

 dogs. Oysters thus transmit typhoid. 



III. The animal may through a bite pro- 

 duce a lesion into which the infectious 

 agent is transferred, as in rabies and espe- 

 cially in the blood-sucking insect diseases. 

 Rat-bite fever, which according to the re- 

 cent work of Hektoen and Tunnicliffe may 

 be caused hy the streptothrix of rat pneu- 

 monia entering the wound caused by the 

 bite of the infected rat, would be here 

 included. 



IV. The parasite may be transmitted to 

 man through the meat of lower animals 

 used as food. It is possible though rare 

 for certain bacterial diseases like tuber- 

 culosis and perhaps paratyphoid fever to be 



