HARDENING OF TISSUE. 531 



The wet and dry specimens are exposed in open Es- 

 march dishes in the room during' the disinfection process. 

 At the close of the period of disinfection, 5, 10, or 20 hours, 

 the room is entered and the covers promptly replaced. 

 Each specimen is then taken up by a pair of forceps and 

 transferred to a tube of bouillon. The forceps must be 

 sterilized in the flame before making each transfer. 



The student will make experiments in the manner indi- 

 cated with anthrax spores, diphtheria and typhoid fever 

 bacilli, and with staphylococci. The results should be 

 carefully controlled as indicated on p. 523. 



Hardeningi Imbedding and Cutting of Sections. 



The direct microscopical examination of streak prepar- 

 ations made from the organs and tissues of infected ani- 

 mals, as well as cultural experiments will, as a rule, reveal 

 the presence of micro-organisms. In order to ascertain the 

 presence and especially the distribution of org'anisms within 

 the tissues and organs it is necessary to harden these, then 

 to cut sections and finally to stain the sections by suitable 

 methods. 



The tissue to be hardened must be cut up into small 

 pieces, about 5-8 mm. in thickness. In special cases even 

 thinner pieces must be used. These are then placed in the 

 fixing, and hardening fluid. It is always advisable to place 

 the pieces of tissue on a piece of filter-paper or on some ab- 

 sorbent cotton. The liquid thus has free access to all parts 

 of the tissue. The fixing and hardening of tissue, which is 

 to be stained for bacteria, is usually done in alcohol, mer- 

 curic chloride or in a formaldehyde solution. Small wide- 

 month bottles should be employed. 



Alcohol. — The pieces of tissue, supported on filter-paper 

 or cotton, are placed direct in 95 per cent. alcohoL They 

 are allowed to remain in this alcohol for 3 or 4 days, after 



