1901] MICROSCOPICAL JOURNAL. 131 
and the eradication of such pests was taken up with en- 
ergy and perseverance. The rarity with which these par- 
asitic pests are encountered among civilized people of the 
present day proves the value of correct views upon such 
questions. . 
The last point to be yielded by the believers in spon- 
taneousgeneration was the origin of the protozoa and bac- 
teria, microscopic animals and plants so small that their 
life history could be studied only with great difficulty. 
_ It was finally shown, however, that even these infinitely 
small organisms obeyed the general law of nature and 
propagated and developed from ancestors, each species 
after its kind, and that in the absence of ancestors not 
even these low forms of life could appear. 
About this time it began to be suspected that the cause 
of the contagious fevers was microscopic organisms, which 
were able to live a parasitic life in the bodies of men and 
the larger animals. After many observations pointing in 
that direction it was finally demonstrated in 1876 that the 
_ cause of anthrax was a bacillus, and shortly afterwards 
that fowl cholera, septicemia, hog cholera, tetanus, black- 
leg, tuberculosis, and various other diseases were due to 
similar microscopic vegetable organisms, each disease be- 
ing caused by its own distinct species of germs. It was 
also shown that malaria, Texas fever, and some other dis- 
eases were caused by microscopic animal organisms be- 
longing to the protozoa, and that here again each disease 
had its own definite and distinct species. In every case 
the minute plant or animal parasite had its own definite 
form and certain biological characters by which it might 
be distinguished from all other living things. Each spe- 
cies multiplies and propagates its kind, and there is no 
more evidence here than elsewhere in nature to sustain a 
doctrine of the spontaneous appearance of living things. 
The first effect of these scientific demonstrations was 
to clear away a vast amount of rubbish which had accu- 
