392 



COLLOIDS IN BIOLOGY AND MEDICINE 



Besides the microorganisms directly visible in the microscope, 

 there are others so small as to be microscopically invisible, and only 

 recognizable by their pathogenic effects. They are, therefore, called 

 ultravisible. Among these are about forty pathogenic germs, among 

 others, smallpox, rabies, measles, scarlet fever and the mosaic disease 



DISINFECTING ACTION OF HALOGEN NAPHTHOLS. 



Lethal action on 



Number of halogen atoms. 



Co// 



Sfaphy/ococcus 



- Diphtheria 



T* Strep /oco ecus 

 ___ Panafypfii/s 



FIG. 52. (See p. 402.) 



of tobacco. The name ultravisible is not a happy one, since recently 

 by dark-field illumination there have been recognized, in the case of 

 many infections, minute organisms, which we are justified in believing 

 to be the cause of the diseases. The ultravisible viruses are not held 

 back by ordinary bacteria filters; recently they have been called 

 filterable microorganisms. 



