374 EXTINCTION OF THE BISON AND WHALES 



are microscopic corkscrew-like creatures, of which many 

 kinds have become known within the last teo or fifteen 

 years. They are " single cells " — that is to say, " proto- 

 plasmic " animalcules of the simplest structure — provided 

 with a vibrating crest and tail by means of which they 

 swim with incessant screw-like movement through the 

 blood. They rarely exceed one thousandth of an inch in 

 length exclusive of the tail. The poisons which they 

 produce by their life in the blood are the cause of the 

 sleeping-sickness of man (in tropical Africa), of the horse 

 and cattle disease carried by the tsetze fly, and of many 

 similar deadly diseases — a separate " species " being dis- 

 covered in each disease. A peculiar species is found in 

 the blood of the common frog, and another in that of the 

 sewer-rat. The last discovery of a " trj'panosome " is 

 that of one in the blood of the African elephant, announced 

 to the Royal Society by Sir David Bruce. 



It is a matter of great interest that a trypanosome has 

 been found in a death-stricken herd of European bison. 

 It suggests that one of the causes of the disappearance of 

 the bison, both in Europe and America, may be the 

 infection of their blood by trypanosomes, and that possibly, 

 whilst a freely migrating and vigorous herd would not be 

 extensively infected, a dwindled and confined herd may 

 •be more liable to infection, and that thus the final destruc- 

 tion of an already decadent animal may be brought about. 

 It would now be a matter of extreme interest to ascertain 

 whether the few dwindled herds of bison in North 

 America are infected by trypanosomes, and no doubt we 

 shall soon receive reports on the subject. 



A most interesting branch of this subject of the un- 

 thinking extermination of great animals by man is that 

 of the extermination of whales. Man is worrying them 

 out of existence. Some are already beyond saving. It 

 would be interesting to know whether there are trypano- 



