Diptera 35 



solution. The drop was allowed to dry, it being thought that the 

 salt crystals would facilitate the grinding up of the glands with the 

 end of a small glass rod, this being done under microscopic control. 

 After grinding up, a small drop of water was added of the size of the 

 original drop of saline, and an equal volume of human blood taken 

 from the clean finger-tip was quickly mixed therewith, and the whole 

 drawn up into a capillary tube. Clotting was not prevented and no 

 hemolysis occurred. Salivary gland emulsion added to a dilute 

 suspension of corpuscles did not lead to hemolysis. This f experi- 

 ment was repeated a number of times, with slight modification, but 

 with similar results. The data obtained from the series "do not 

 support the hypothesis that the salivary glands, at any rate in Culex 

 pipiens, contain a substance which prevents coagulation." 



Much more detailed, and the more important experiments made 

 along this line, are those of Schaudinn (1904). The results of these 

 experiments were published in connection with a technical paper 

 on the alternation of generations and of hosts in Trypanosoma and 

 Spiroch&ta, and for this reason seem to have largely escaped the notice 

 of entomologists. They are so suggestive that we shall refer to them 

 in some detail. 



Schaudinn observed that the three cesophageal diverticula (com- 

 monly, but incorrectly, known as the "sucking stomach") (fig. 24) 

 usually contain large bubbles of gas and in addition, he always found 

 yeast cells. On the ground of numerous observations, Schaudinn 

 was convinced that these yeast plants are normal and constant 

 commensals of the insect. He regarded them as the cause of the gas 

 bubbles to be found in diverticula. It was found that as the insect 

 fed, from time to time the abdomen underwent convulsive contrac- 

 tions which resulted in the emptying of the oesophageal diverticula and 

 the salivary glands through blood pressure. 



In order to test the supposed toxic action of the salivary glands, 

 Schaudinn repeatedly introduced them under his skin and that of 

 his assistant, in a drop of salt solution, and never obtained a sugges- 

 tion of the irritation following a bite of the insect, even though the 

 glands were carefully rubbed to fragments after their implantation. 

 Like Nuttall, he failed to get satisfactory evidence that the secre- 

 tion of the salivary glands retarded coagulation of the blood. 



He then carefully removed the cesophageal diverticula with their 

 content of yeast and introduced them into an opening in the skin 

 of the hand. Within a few seconds there was noticeable the charac- 



