1894 THE MICROSCOPE. 37 



ual may take this disease through an open wound, or an 

 abrasion of the skin ; but the respiratory tract furnishes 

 the best medium for infection. A very common mode 

 of infection, especially in children, is from the ingestion 

 of milk from cows affected with tuberculosis. The tem- 

 perature for the growth of this germ is 99° F., and they 

 multiply slowly. The thermal death-point is 160° F. 



The bacillus of diphtheria is the specific germ of that 

 dreaded disease, diphtheria. They are rod shaped, 

 straight or slightly curved, with rounded, club-shaped 

 ends, having a length of 1-10,000 of an inch, and a diam- 

 eter of 1-40,000 of an inch. Infection may take place 

 from inhaling the poison, or where there is an abrasion 

 of the skin ; also from the food taken, and especially milk, 

 which is a favorable medium for the growth of this ba- 

 cillus. The development takes place at a temperature of 

 from 70° to 107° F. ; the most favorable temperature is 

 95° F. The thermal death-point is 140° F. The diph- 

 theria germs have a great tenacity for life, may remain 

 virulent for many months and tolerate the exposure to 

 rain and sunshine during the months of April and May. 



The micrococci of pneumonia are spherical or oval, 

 usually united in pairs, or in chains consisting of three or 

 four elements, which are srruounded by a transparent 

 capsule. In length they are about 1-25,000 of an inch; 

 diameter 1-35,000 of an inch. Infection from this micro- 

 coccus takes place through the medium of the respiratory 

 passages. These germs are found in the saliva and nasal 

 secretions in many persons in good health for days and 

 weeks at a time, — perhaps they are waiting for the lungs 

 to become irritated from a cold or from epidemic influ- 

 enza so that it may cause its ow^n specific disease, pneu- 

 monia. Blood heat, 98° F., is most favorable for their 

 growth. The thermal death-point is 130° F. 



The bacilli of typhoid fever have an average length of 

 1-12,000 of an inch, and a breadth of 1-40,000 of an inch, 



