of Bacteria and their Allies by Heterogenesis. 383. 
Whenever, therefore, Bacteria or their allies appear in the 
midst of the tissues or fluids of animals or plants, two possi- 
bilities have to be considered in order to account for their 
presence. The two questions that have to be asked are 
these :— 
(a) Are the bodies of plants and animals interpenetrated 
in all parts by invisible germs of microorganisms, or are they 
germless ? 
(0) Have the microorganisms which may be found in the 
tissues or fluids of plants and animals under various conditions 
been produced therein by heterogenesis (possibly in the fluids 
by archebiosis), or is their presence invariably to be ascribed 
to infection from without ? 
(a) During the last thirty years it has been commonly 
held, in accordance with the teachings of Pasteur, Lister, and 
others, that the tissues and fluids of healthy animals and plants 
are germless and altogether free from microorganisms, 
In regard to animals, however, it is clear that this position 
is one which cannot be accepted without very important limi- 
tations. It is obvious that microorganisms may, like other 
particles, get taken up from the mucous membranes of the 
alimentary canal and the respiratory system, and pass by 
means of lymphatics into the nearest glands. If they should 
get through these and ultimately pass into the blood, the 
generally accepted view is that they are speedily destroyed in 
this fluid. ‘This view is based upon the fact that bacteriolo- 
gists are never able to get evidence of the existence of micro- 
organisms or their germs by the inoculation of different 
suitable and sterilized media, with blood drawn from a healthy 
man or from one of the lower animals similarly free from 
disease. 
Yet, although the blood and internal tissues of healthy 
animals and of man are declared to be free from micro- 
organisms and their germs, such organisms will habitually 
show themselves after death, in the course of a tew days, 
throughout all the organs, even when life has been abruptly 
terminated in a state of health. It cannot reasonably be 
said in explanation of this that the organisms naturally 
present in the intestinal canal have been enabled to spread 
through the body so as to reach the most remote parts after 
death, since many of the organisms are motionless and others’ 
exhibit. mere to-and-fro movements of a non-progressive 
character. The blood, again, has ceased to circulate, so that 
this fluid, germless during life, cannot after death be con- 
sidered to act as a carrier. But if the organisms themselves 
cannot make their way through the tissues and travel far 
