796 CHEMOTHERAPY 



It is not necessary to describe the earlier methods, because these are 

 now largely only of historic interest, and it is quite generally accepted, 

 from the point of view both of efficient treatment and of the comfort of 

 the patient, that the intravenous injection of a dilute solution of the di- 

 sodium salt is the best form of administration. For this reason I shall 

 briefly mention the other methods, and describe the method of intraven- 

 ous injection of the alkaline solution in greater detail further on. 



The Acid Solution. When salvarsan is dissolved in warm water or 

 warm normal saline solution, a strongly acid solution is obtained. In 

 this form the drug is most irritating and also most toxic, and when in- 

 jected subcutaneously and intramuscularly, produces severe pain and 

 necrosis. This method is seldom if ever used at the present time. 



The Mono-acid Solution. If to the watery acid solution half the 

 amount of alkali necessary to produce complete neutralization is added, 

 a solution of the mono-acid compound will be formed. This solution 

 has been given intramuscularly, but is also extremely irritating. 



The Neutral Suspension. This is the drug in the form of a precipi- 

 tate of the base, prepared by adding to the original acid solution just 

 sufficient caustic soda to neutralize it. The method was devised by 

 Michaelis and Wechselmann, and for some time was the form of adminis- 

 tration most generally employed for subcutaneous and intramuscular 

 injection. It is probably less irritating than the acid and clear alkaline 

 solution, but occasionally there resulted encapsulation of masses of ne- 

 crotic tissue containing considerable quantities of arsenic. 



Other Suspensions. Suspensions of salvarsan in liquid paraffin, 

 sterile olive oil, oil of sesame, or almond oil are said to keep for some 

 time if placed in dark containers. This cannot, however, be always de- 

 pended upon, and the slightest decomposition of the original drug is 

 capable of producing marked toxic symptoms. These suspensions are 

 said to be comparatively non-irritating, but they may cause local necrosis 

 of tissues, and on account of their slow absorption, only small amounts 

 gain access to the general circulation at one time. 



This method may, however, be of value, especially in infants and in 

 cases where slow absorption is desired in order to prolong the effect of 

 the drug. Analgesics, such as eucain, creosote, or an essential oil, may be 

 incorporated in the suspension in order to lessen the pain. 



The suspension is so prepared that each cubic centimeter contains 

 0.1 gram of the drug. 



Alkaline Solution of the Disodium Salt. This is the form in which the 

 drug should be administered by intravenous injection. It is this solu- 



