MODE OF INFECTIO]^ 313 



Low, whose paper was published first, stated that the filarige reached the 

 human host " not along the salivary duct as is the case with the malarial para- 

 site, for this channel is manifestly too minute to accommodate a body relatively 

 so gigantic as the filaria ; not along the oesophagus or pharynx, as Bancroft sug- 

 gested ; but by making an independent passage through the base of the labium, 

 and pushing forwards along the proboscis between labium and hypopharynx 

 amongst the stylets." Low was correct in his statement that the filaris do not 

 leave the mosquito by the salivary ducts or oesophagus but he was mistaken, as 

 we shall see, in the manner of their escape. The error was due to faulty inter- 

 pretation, as his own illustrations, from his microscopic preparations, show. 



James, a little later in the same year, as the result of experiments in India 

 with filaria-bearing mosquitoes, announced that he had found the ripe larvae 

 inhabiting the labium. Throughout his paper he employs the term " labrum " 

 instead of labium, but reference to his figures shows that this is a lapsus and that 

 he had found the true condition. In consequence he accepted the doctrine of the 

 transmission of filarise direct by the mosquito, which he had up to then opposed. 

 He procured further evidence by observing the behavior of filarige, taken from 

 the mosquito, when placed in water and in blood. He found that those larvse 

 which had been placed in water soon became slower in their movements, and, 

 after two and a half hours were dead. Those placed in blood retained their 

 activity undiminished for a long time and lived fully seven hours. 



In papers published still later in the same year Grassi and Noe verified that 

 the ripe filarial larvae inhabit the interior of the labium and there wait until 

 the mosquito bites to migrate to their ultimate host. They supposed that when 

 the labium was doubled upon itself in the act of biting a tension of this organ 

 was produced which caused it to rupture along the dorsal groove and liberate the 

 filarige. They believed that they had detected a labium thus ruptured among 

 their preparations. 



Finally, in 1901, the true method of escape of the filarige from the labium was 

 indicated by Annett, Button and Elliott, although they were unable to demon- 

 strate it. These authors studied carefully the mouth-parts of the mosquito and 

 found that dorsally at the tip of the labium and connecting the labellge there is 

 a delicate membrane and that this is the weakest point in the labium. They 

 showed that the filarise most probably made their exit at this point, not only 

 because it is the weakest, but also because the path of the filarige lay in this 

 direction and they were often found in the anterior portion of the labium. 

 The membrane in question has been termed, in honor of one of these investi- 

 gators " Button's membrane.*' 



That this last explanation is the correct one was not demonstrated until 1905, 

 when Dr. Mario G. Lebredo, of Havana, published the results of his investiga- 

 tions. Lebredo was not only able to show that the filarial larvae escape by pierc- 

 ing the delicate membrane at the tip of the labium, but also that this does not 

 happen when the mosquito sucks water, sweets or vegetable juices — a suggestion 

 which had been previously made but generally rejected. 



