72 



This lake is formed by the sewage from the city of San Antonio, 

 and certain portions of its margins seemed to offer excellent 

 breeding places for malarial mosquitoes. The bats were success- 

 fully established in this building, and at the time of one of 

 Mr. Bishopp's visits, August 26th, 1914, the emergence flight 

 of the bats was noticed. He estimated that not to exceed nine 

 thousand bats emerged, although Doctor Campbell estimated 

 that the house is capable of accommodating two hundred and 

 fifty thousand bats. At the time of this visit the amount of 

 guano which had accumulated was almost negligible. 



The district about Mitchell Lake is not within the corporate 

 limits of San Antonio, and the cases of malaria had not been 

 reported, so that no statistics are available to determine the 

 relative prevalence of the disease before and since the construc- 

 tion of the roost. Inquiry which Mr. Bishop made among the 

 employees of the land company, with headquarters at the lower 

 end of the lake about three miles from the roost, seemed to show 

 that there was no apparent difference in the abundance of 

 mosquitoes or the prevalence of malaria before and after the 

 construction of the roost. In all cases the inhabitants reported 

 mosquitoes to be extremely abundant, and the company's store 

 reported that there was a good demand for chill tonics. Around 

 the head of the lake, near the bat roost, the Mexicans interviewed 

 reported favorably on the effect of the roost. Mr. Bishopp, 

 however, made an examination of the premises of one of these 

 Mexican tenants, about one-third of a mile from' the roost, and 

 found that mosquitoes were present in exceedingly large numbers. 

 They were hidden in the dark corners of the chicken house and 

 the calf pen, but no examination was made of the dwelling. All 

 were Anopheles pseudopunctipennis. It appears from, Mr. 

 Bishopp's report that San Antonio is in a region where bats are 

 normally extremely abundant. The prevalent species is the free- 

 tailed bat, Nyctinomus mexicanus, a species which roosts in great 

 numbers in deserted houses in large numbers in that vicinity, and 

 the numerous caves among the hills several miles away furnish 

 suitable breeding places for great numbers, which come into the 

 plains nightly for the purpose of feeding. The report further 



