LABORATORY STERILIZATION 247 



Tincture of lodin. In vitro, tincture of iodin is of little value as a 

 germicide, but freshly prepared tincture of iodin applied to the skin 

 appears to possess very considerable germicidal value. This solution 

 seems to be most effective when it is freshly prepared and works most 

 satisfactorily when the part upon which it is to be used has been 

 cleaned with alcohol and allowed to dry. Nascent iodin is liberated, 

 and it is stated that iodin in statu nascendi is the active germicidal 

 factor. Tincture of iodin is rather widely used as a skin disinfectant 

 for minor operations, for sterilizing the epidermis prior to spinal 

 puncture, collecting blood for cultural purposes, and for operations 

 upon laboratory animals. Iodin is absorbed through the skin, and 

 in large amounts it is toxic. 



Boric Acid. Boric acid is frequently used upon mucous surfaces 

 and other exposed parts when a very mild antiseptic solution is 

 required. Boric acid is rather an antiseptic than a germicide: its 

 chief advantage lies in the fact that 1 to 3 per cent, aqueous solutions 

 have but little action on the tissues. 



All disinfectants appear to be cellular poisons to a greater or lesser 

 degree; in lesser concentrations they are without marked effect upon 

 microorganisms; in effective concentrations they appear to form 

 combinations with tissues if they are used in or on man. 



Disinfection of the tissues has been attempted with specific bac- 

 tericidal sera, which are without noteworthy harmful effects upon 

 the patient. At the present time immune sera are not wholly satis- 

 factory for this purpose, but sufficiently encouraging results have 

 been obtained to justify their present use and to afford promise of 

 their improvement in the future. 



A majority of chemical disinfectants are, to use Ehrlich's termin- 

 ology* organotrophic rather than parasitotrophic, that is, they have a 

 greater affinity for the tissues of the host than for the parasite. Quinine, 

 on the contrary, appears to be parasitotrophic it is almost a specific 

 for malarial parasites. Ehrlich's brilliant researches in chemotherapy 

 have added organic compounds containing arsenic to the list of para- 

 sitotrophic substances; they have a very direct and inimical action 

 upon trypanosomes and the Treponemata, and but minimal action 

 upon the tissues of the host. 



Formaldehyde. A solution of formaldehyde gas in water, commer- 

 cially known as formalin, is a powerful disinfectant; it does not react 

 as strongly as mercuric chloride with protein solutions; 1 it does not 



1 Formaldehyde unites with ammonia and with the amino-nitrogen of amino acids to 

 form stable compounds; there is relatively little action upon native proteins, however. 



