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SCIENCE 



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



only appears to be true because we know 

 more about the diseases of man than those 

 of the lower animals. 



Certain reasons may be here enumerated 

 why man is subject to at least many of the 

 animal diseases. Man is commonly con- 

 cerned in caring for sick animals and some 

 diseases, like glanders, are commonly trans- 

 mitted in this way to veterinarians, host- 

 lers and teamsters. The demand of the 

 human for animal pets and the social de- 

 mands of certain types of humanity for 

 dogs, cats and other animals living in inti- 

 mate association with them explains the 

 origin of certain diseases, especially those 

 parasitic in character. Man lives largely 

 on meat and other animal products, many 

 of which are uncooked or improperly 

 cooked. Man uses animals in a variety of 

 ways in the industries, the relations being 

 often such as to necessitate intimate con- 

 tact. Again, wild animals are free from 

 many diseases but domestication or confine- 

 ment by man may make them highly sus- 

 ceptible. Such animals then may become a 

 source of danger to man and thus a vicious 

 circle is established. 



The transfer of certain diseases from ani- 

 mals to man is, under existing conditions, 

 not a reversible process. Rabies is com- 

 monly transmitted from dog to man but 

 practically never, so far as we know, in the 

 reverse direction. This is true of many dis- 

 eases and depends upon such factors as the 

 superior care given to the human sick and 

 the methods of isolation. 



It would seem then that man's relations 

 and points of contact with a large variety 

 of the lower animals are more intimate and 

 complex than those of any of the other ani- 

 mals to other species and as a result of such 

 relations, on the whole, the disease trans- 

 mission from animals to the human is nat- 

 urally increased in number and variety. 

 This is one of the penalties that man pays 



for being nurse, doctor and master of the 

 brute creation. 



While animals play such a very impor- 

 tant role in the transmission of disease to 

 man it is interesting to note that plants 

 play practically no role whatsoever in this 

 regard. Though plants are afflicted with 

 microbic and fungous diseases to an extent 

 probably even greater than are animals, 

 only one organism is known which is ap- 

 parently pathogenic for both plants and 

 man. According to the work of Johnston, 2 

 cocoanut budrot, a disease of the cocoanut 

 common in Cuba, is caused by an organism 

 practically identical with Bacillus coli 

 (Escherich) Migula. Inoculations into co- 

 coanut seedlings with B. coli of animal 

 origin give infections similar to inocula- 

 tions with the cocoanut organism. It may 

 be stated, however, that this plant disease 

 is of no significance, so far as we know, in 

 the transmission or the causation of human 

 disease, since B. coli ordinarily does no 

 harm when taken into the alimentary canal. 

 It is true, of course, that many plants carry 

 disease germs such as typhoid and dysen- 

 tery bacilli mechanically upon their sur- 

 face where they may remain alive for some 

 time and in this respect play a role com- 

 parable to that of flies in the transmission 

 of typhoid fever. 



The higher plants being so remote bio- 

 logically from the higher animals it is im- 

 probable that specific disease germs patho- 

 genic to these two types of organisms will 

 be found. However it is possible that 

 plants may be found which serve as inter- 

 mediate hosts for organisms not pathogenic 

 for them but pathogenic for certain ani- 

 mals. Many of the viruses and parasites 

 which cause disease in man use some lower 

 form of animal biologically far removed 

 from man for a certain period of their de- 



2 ' ' The History and Cause of the Cocoanut Bud- 

 rot," Bull. No. 228, Bureau of Plant Industry, 

 1912. 



