July 16, 1915] 



SCIENCE 



93 



has been displayed in recent years. Most of 

 the European nations whicli have possessions 

 in Africa have sent scientific expeditions to 

 that continent to study the insect-borne dis- 

 eases. In the case of England, the Royal So- 

 ciety, the Imperial Bureau of Entomology, and 

 the great schools of tropical medicine have sent 

 such expeditions. As there has been an urgent 

 demand from administrative officers and others 

 for early information on the subject of African 

 insect-borne diseases, many of the commissions 

 and investigators have published preliminary 

 or progress reports from time to time. The 

 undertaking of the author of this book was to 

 summarize and correlate as far as possible the 

 findings of the different investigators which 

 in many cases have not been harmonious. Dr. 

 Hindle himself has conducted investigations 

 in various parts of Africa and adds his own 

 views to those of other investigators on points 

 which are by no means settled. 



The general plan of the work is to combine 

 the necessary entomological and medical fea- 

 tures of the problem so that the accounts of the 

 different diseases will be complete. In the 

 treatment of diseases borne by mosquitoes, for 

 instance, a full discussion of the classification 

 of the mosquitoes is given. This is followed by 

 a series of chapters on the diseases such as 

 malaria and yellow fever which these insects 

 transmit. The completeness of the work may 

 be judged from the table of the two hundred 

 and forty-one species of anopheles, their classi- 

 fication and generic synonymy, and notes on 

 their habitat and connection with m.alaria. 

 Even with such complete special discussions 

 the work is well balanced, but its chief char- 

 acteristic is its inclusiveness and the good 

 judgment the author has displayed in the ex- 

 clusion of immaterial details. 



Dr. Hindle lost his life in military opera- 

 tions in Africa, where he was continuing his 

 investigations of tropical diseases, soon after 

 the outbreak of the war. He was a young man 

 and would undoubtedly have made further 

 valuable contributions to the study of insect- 

 borne diseases. But the present book may be 

 considered a monument that will mark his 

 place, which was an important one in the study 



of tropical diseases at a time when such work 

 as his was much needed. W. D. Hunter 



SPECIAL ABTICLES 



THE DIFFUSION OF GASES AT LOW PRESSURES 



MADE VISIBLE BY COLOR EFFECTS 



An interesting and instructive experiment 

 for the lecture table is to connect a discharge 

 tube AC, which is about one meter or more 

 in length and which has the exhaust nipple at 

 one end, to a pump that will give a Geissler 

 vacuum — an oil Geryk pump will answer very 

 well. Between the pump connection M and 

 the valve that closes the tube there should 

 be fused a side branch N also having a valve. 

 Connect iV by a rubber tube to some source of 

 gas other than air, e. g., ordinary illuminating 

 gas. The connection at M should be made 

 direct to the pump. Connect A and to the 

 terminals of an induction coil that will give 

 a spark in air five or more centimeters long. 



To operate, close the valve in the branch N, 

 open and evacuate the discharge tube to 

 the point where on sparking the characteris- 

 tic strife show distinctly. It is immaterial 

 whether A or C is the cathode, or whether the 

 discharge is unidirectional. Now close the 

 valve 0, and, with the pump still running, 

 open N partly, allowing illuminating gas to 

 be drawn by the pump through the branch 

 OM, thus displacing the air by the gas. By 

 closing N, pumping and later admitting more 

 gas, every trace of air may be washed out of 



"€ 



•Sii! 



Fig. 1. 



the tube leading up to 0. Now with N closed 

 allow the pump to run for a few seconds untO. 

 it is judged that the pressure in the connect- 

 ing tube MO is about that in the discharge 

 tube AO. 



At this stage everything is in readiness for 

 the experiment, namely, the diffusion of gases 

 at low pressures made visible by the color ef- 

 fect. The well-known characteristic color of 

 the discharge in the case of residual air< con- 



