436 



NA TURE 



[September 22, 1923 



arrangements will be published when we have com- 



ftlcted the examination of the long-range particles 

 rem the active deposits of actinium and thorium. 



L. F. IUtks. 

 J. Stanley Rogers. 

 Cavendish Laboratory, Cambridge, 

 September 15. 



The Intermediary Hosts of the Human Trematodes, 

 Schistosoma haematobium and Schistosoma 

 mansonl in Nyusuland Protectorate. 



I HAVK received a letter enclosing two tubes con- 

 taining specimens of five species of fresh-water 

 molluscs from Capt. W. H. Dye, Medical Officer, 

 Karonga, Nyasaland, British Central Africa. Capt. 

 Dye writes : " I think I can say that the enclosed 

 specimens represent all the fresh-water molluscs to 

 be found in this district, as I have searched most 

 thoroughly." 



Capt. Dye was able to infect two of the species 

 experimentally with Schist, hcematobium and Schist, 

 matisoni respectively. 



The molluscs have kindly been identified as follows 

 by Mr. G. C. Robson, Zoological Department, Natural 

 Histor>' Museum, S. Kensington. 



( i) Lanistes ajffinis, Smith (full grown and young). 



(2) Vivipara robertsoni, Frauenfeld. 



(3) Limn<Ba natalensis, Krauss. 



(4) Physopsis sc. globosa, Morelet. 



(5) Planorbis sp. near sudanicus, Martens. 



Capt. Dye writes of (4) Physopsis sc. globosa, 

 Morelet : " They are very common in the marshy 

 pools, although rather difficult to find owing to their 

 predilection for the muddy undersides of reeds, etc., 

 and their habit of dropping off when the plant is 

 touched. They appear to attract S. hcEtnatobiutn 

 readily, and large numbers of miracidia disappear 

 out -of the tube in which they are put, against the 

 control." 



Capt. Dye goes on to describe in detail the experi- 

 ments he made. He finds that the mollusc dies in 

 two days when heavily infected with the miracidia 

 of Schist, hcematobium, after taking precautions to 

 keep the water as free from decomposition matter as 

 possible. The experiments were repeated several 

 times with the same results. The snails were " not 

 killed by Schist, mansoni, but one cannot get such 

 concentration of eggs from faeces as from urine." 



As to Planorbis sp. near sudanicus. Martens, it is 

 referred to as " the one and only species of planorbis 

 in this part of the world (I have most thoroughly 

 searched). This species is not killed by a heavy 

 infection of Schist, hcematobium," but was " infected 

 from a good heavily infected stool with Schist, 

 mansoni." 



Capt. Dye sent specimens of infected snails, but they 

 died en route and were too decomposed for sectioning 

 on arrival. He appears to have discovered that 

 Physopsis sc. globosa, Morelet, is the intermediary 

 host of Schistosoma hcematobium in Nyasaland, and 

 possibly he has also found the intermediary host for 

 Schistosoma mansoni in Nyasaland {Planorbis sp. near 

 sudanicus. Martens). 



The other snails which he sent had, he stated, no 

 attraction for either Schist, hcematobium or mansoni. 



J. B. Christopherson. 



London, W.i. 



The One-Host Life-Cycle of Hymenolepis fratema. 

 Stiles, of the Mouse. 



In the recently issued third volume of " The Prac- 

 tice of Medicine in the Tropics," edited by Byam and 

 Archibald, Drs. Clayton Lane and Low call in question 



NO. 2812, VOL. 112] 



>ix>n the 

 i it is of 



.,< 



(on pp. 1821-2) the one-host ;i 

 of tne well-known tapeworm 

 Stiles. This account is principal 

 work of Grassi and Kovelli .nnd J" 

 considerable interest and i' 

 the facts, not only bccau.s- 

 worms in the higher anin 

 two hosts in order to ca>- 

 also because thes. ' • ' 

 the problem con^ 

 Hymenolepis nana m m.m 



To ascertain the truth of the matter I have during 

 the last three months selected from a large nn'"»>^-'^ -f 

 tame mice thirty-four individuals which I i 

 under close observation for jjcricwls \:irviii 

 33 and 55 days, during which the f 1 

 no Hymenolepis eggs, and from win 

 eluded that the mice were free from HymenoKjus 

 infection. On July 20 I infected twenty of tl)<^<- 

 mice with large numbers of Hymenolepis <*;.:us 

 obtained from naturally-infected mice, leaving; i!:-- 

 other fourteen mice as controls. Of the tw ■ 

 infected, eighteen were found to contain ci 

 various stages of development when examined il^ w, 

 five to twenty-four days after, one (examined onlv 

 three days after) probably contained cysticeroids, and 

 one only had apparently remained uninfected. The 

 controls remained uninfected. Since these experi- 

 ments were conducted under conditions which ren- 

 dered it impossible for fleas, house-flies, or other 

 animals to serve as intermediate hosts, and since all 

 other necessar)'' precautions were taken, it must be 

 concluded that the one-host account of the life-cycle 

 of Hymenolepis fratema is the correct one. The 

 details of these experiments will be published in full 

 at the earliest opportunity. 



W. N. F. Woo 



Wellcome Bureau of Scientific Research, 

 London. 



Polar Climate and Vegetation. 



Dr. Stefansson's proposition, as put forth in his 

 letter to Nature of August 4, p. 162, that if either 

 pole of the earth were situated in a lowland area the 

 winter snowfall would be insufficient to produce a 

 permanent ice-cap, is fundamentally based uf>on the 

 fact that the Arctic lowlands of Canada and Siberia, 

 with a mean annual temperature far below the freezing- 

 point, are yet free from a summer snow-cover and 

 permanent glaciation. This proposition is tanta- 

 mount to saying that the inner north j>olar area is 

 permanently glaciated because it happens to be sea, 

 and the south polar area because it hapi>ens to be a 

 plateau 10,000 feet high. 



That this is essentially a sound conclusion will, I 

 think, appear on a little reflection. Around the North 

 Pole sea-ice forms during the six months night in 

 such quantity that barely half of it can be melted 

 during the six months day, with the consequence 

 that even in July the mean air temperature (as given 

 by Mohn) does not rise above -f 30° F.. or 2° below the 

 freezing-point, while the mean January temperature 

 drops to -40° F. — an extreme " continental " range 

 of temperature at a low general level conditioned by 

 the vast expanse of floe-ice amounting to some two- 

 thirds of the area of the polar sea. On the other 

 hand, the mean July temperature of the Arctic 

 lowlands varies with locality between 40° and 60° F., 

 and, as pointed out by Dr. Stefansson, heat spells of 

 90° in the shade commonly occur. 



The great summer cold of the Antarctic Plateau 

 is at first sight more difficult to understand than the 

 less severe summer cold of the Arctic Ocean. The 



