44 Lectures on Bacteria. [§ v. 



plants through the open slits in the epidermis, the stomata, which 

 lead to the system of intercellular passages. It is probable that this 

 actually takes place, but it is not yet quite certain and requires 

 further investigation. The respiratory and alimentary canals in 

 healthy, especially warm-blooded, animals are constantly acces- 

 sible places for the entrance of germs with air, meat and drink, 

 and it is these parts, especially the mouth and the intestinal 

 canal, both in man and other warm-blooded animals, which are 

 as a matter of fact always a well-stocked garden of vegetating 

 Bacteria. They may also make their way into the glands which 

 are in communication with these canals through their excretory 

 ducts. Researches into their occurrence in the blood of healthy 

 living warm-blooded animals give diiferent results. Hensen, 

 Billroth, and other observers maintain their presence there. Very 

 careful investigations by Pasteur, Meissner (13), Koch, Zahn, 

 and others give a negative result; the affirmative result may 

 therefore be due to disturbances and errors in the experiment. 

 But this conclusion is not unavoidable, for a series of experi- 

 ments by Klebs (12) have placed it beyond doubt that both 

 states may occur, and why they may occur. Klebs examined 

 the blood of some dogs, and partly with a negative result. But 

 in the case of one dog the result was aflSrmative, the fact being 

 that putrefactive Bacteria had been injected into the blood of 

 this animal some time before on the occasion of some other 

 experiments ; it had sickened with them but had quite recovered 

 long before the date of the investigation of which we are now 

 speaking. It cannot be doubted that in this case germs capable 

 of development but actually dormant had remained from the 

 first experiment in the animal's blood, and we may conclude 

 generally that Bacteria germs may be present in healthy blood, 

 if they have once made their way into it through a wound or in 

 some other way. 



The result of the above facts is to show the wide distribution 

 and great abundance of Bacteria-germs, though their species 

 are not at present clearly discriminated. They show also on 



