SLEEPING SICKNESS 265 



When the tsetse fly, Glossina palpalis, feeds on a man in whose peripheral circu- 

 lation there are normal type trypanosomes we have an accumulation of such forms in 

 the middle and posterior portions of the gut. From the eighth to the eighteenth day 

 long, slender forms develop and pass forward into the pro ventriculus. None of the in- 

 testinal forms can cause infection when injected into animals. These proventricular 

 types work their way into the salivary ducts and thence into the salivary glands, 

 where further development takes place. Here we have shorter forms developing, 

 which are similar in morphology to the normal blood type. It is at this stage that 

 the fly becomes infective by the passing of these trypanosomes down the salivary 

 ducts and through the channel in the hypopharynx to the subcutaneous tissues of 

 the person bitten. High temperatures, 75 to 8sF., are favorable to development, 

 while low temperatures, 60 to 7oF., are inimical to development, but do not kill 

 the ingested trypanosomes. This explains the long period which at times elapses 

 before a fly becomes infective. Under favorable conditions a fly becomes infective 

 in twenty to twenty-four days and remains infective the rest of its life, up to 185 days. 

 The infection is not transmitted to the pupa. This is an inoculative, cyclical or 

 indirect type of infection. It is usually considered that a tsetse fly whose proboscis 

 has just been contaminated with trypanosome blood is capable of transferring the 

 infection for a few hours. This would be a mechanical or direct method of infection 

 and such power for infection only lasts for a few hours. 



When tsetse flies feed on animals infected with trypanosomes only 

 from 2 to 6% become infective. Again, it has been shown that where 

 the wild animals on which tsetse flies feed may show an infection of 

 from 16 to 50% yet not more than two out of every 1000 tsetse flies, 

 caught and tried out on susceptible animals, show themselves infective. 



Both of the human trypanosomes of Africa have been cultured by using the 

 N.N.N. medium in which rat's blood was substituted for that of the rabbit. Human 

 blood will also serve as a substitute. Growth however is not constant. 



For the laboratory diagnosis we may use peripheral blood with some 

 thick film method. The examination of preparations from the per- 

 ipheral blood is usually very discouraging. Very much better results 

 (in fact some prefer this method to any other) can be obtained by tak- 

 ing 10 to 20 c.c. of blood into about 25 c.c. of citrated salt solution, 

 centrifuging two or three times and examining the sediment of the 

 third centrifugalization. Button and Todd prefer to centrifuge 

 citrated blood and to collect the leukocyte layer for examination as is 

 done in opsonic work. 



The English workers usually prefer the gland puncture method, using a sterile 

 but dry hypodermic needle. Water in the needle distorts both leishman bodies and 

 trypanosomes. 



In the sleeping sickness stage trypanosomes can almost constantly be found in the 

 cerebrospinal fluid. 



