July 25, 1918] 



NATURE 



405 



have been crippled ; the Association has now to draw 

 on its very limited capital. The committee took the 

 view that, as an Imperial people, it is our duty to 

 shoulder our responsibilities and develop the resources 

 of the Empire — resources of knowledge as well as 

 resources of material — in time of war as well as in time 

 of peace. We are too apt to make war an excuse for 

 postponing our immediate duty. Sir Thomas Wright- 

 son, Bart., has given 50^., but it does not seem too 

 much to expect that three other subscriptions of equal 

 amount mav be placed at the disposal of the 

 Research Committee for Archaeological Investigation 

 in Malta, in addition to the grant from the British 

 Association. The labour conditions in Malta are at 

 present favourable for the continuance of this kind 

 of Imperial undertaking, and the men who are in 

 charge have the skill and experience to employ to the 

 best advantage the modest sum here asked for. 

 Arthur Keith, 

 President, Section H (Anthropology) of the 

 British Association. 



A Successful Method of Obtaining Amoebae for Class 

 Purposes. 



Zoological departments in all parts of the British 

 Isles have experienced, during the last few years, con- 

 siderable difficulty in obtaining a good supply of 

 Amoeba proteus for class purposes at the proper time, 

 the usual hunting-grounds for this organism failing, 

 for some reason or other, to yield their former 

 abundant supply. 



The difficulty was overcome in this de{>artment 

 during the present session by making use of amoebae 

 obtained from soil by a suitable culture method, the 

 outcome of the writer'- work on soil protozoa. This 

 method has proved so successful that it has been 

 thought desirable to give a brief account of it, 

 especially as it has come to my knowledge that other 

 zoological departments are desirous of trying it. A 

 somewhat similar method of obtaining amoebae for 

 class purposes has been in use for some years in the 

 University of California, and has been described by 

 Kofoid in the Trans. Amer. Micro. Soc, vol. xxxiv;, 

 October. 1915. 



For the cultivation of amoebae from soil a liquid 

 medium is preferable to a solid one, such as nutrient- 

 bouillon agar, frequently used for amoeba cultivation, 

 owing to the fact that one frequently finds on a solid 

 medium amoebae with two or more nuclei and various 

 other abnormaltties not found in amcebse from a liquid- 

 culture medium. 



One per cent, hay-infusion is a very useful medium, 

 and is constantly used here. It is prepared as 

 follows : — Ten g.-ams of chopped hay are put into a 

 beaker or flask with one litre of distilled water, and 

 steamed for about three-quarters of an hour ; filter, 

 and then make the filtrate just alkaline by the addi- 

 tion of a sufficient quantity of raustic-soda solution 

 TN.NaOH solution is quite suitable) to make a strip 

 of red litmus paper turn a bluish tint when immersed 

 in the liquid. Sterilise in the autoclave, and, when 

 cold, pour a small quantity into three or four Petri 

 dishes until the liquid is a few millimetres in depth, 

 and inoculate each with soil; about half a gram is 

 sufficient soil for each plate. Almost any kind of 

 soil will serve— garden or field soil. 



Put the dishes aside for a dav or two, either in an 

 incubator at 2o°-2!;° C, or on the laboratory-table, 

 away from direct sunlight, and then examine under 

 the microscope for amoebae. The latter are, as a rule, 

 of the liwax type, and are generally to be found on 

 the surface or at the bottom of the culture. 



Ciliates and flagellates will also be found in con- 



NO. 2543, VOL. lOl] 



siderable numbers; in fact, the ciliates frequently pre- 

 dominate in the early days of the culture, and only 

 when they become less numerous do the amoebae 

 increase in numbers. 



For the purposes of examination clean cover- 

 slips may be dropped on to the surface of the culture- 

 liquid, and then removed to slides and examined under 

 the microscope ; or a platinum loopful^ or two of the 

 surface layers rhay oe taken and put on a slide and 

 then covered with a clean coverslip. When most of 

 the amoebae are at the bottom of the culture, as some- 

 times happens, they are more difficult to remove to 

 slides, but they may be sucked up by means of a 

 capillary pipette gently moved over the bottom of the 

 dish and then transferred to the slide. The coverslips 

 should be sealed with vaseline or wax to prevent 

 evaporation. 



The amoebae vary in size from very small forms, 

 which are not of much service for class purposes, to 

 fairly large forms, which are quite admirable, showing 

 great amoeboid activity and revealing clearly under the 

 higher powers of a junior-class microscope the differen- 

 tiation between ectoplasm and endoplasm, the nucleus, 

 and the streaming of the protoplasm during the pro- 

 gression of the amoeba. Such forms may measure any- 

 thing from 20fx--6ofx in length, according to the 

 degree of extension of the body, and even larger forms 

 may be met with. The organism which has been 

 obtained in practically pure mixed culture here, and 

 has proved so useful, measures between 30 ,u and 50 ,u 

 when extended. The cyst has a diameter of 16 ft- ly fi. 



Having obtained a gcod-sized form, one should 

 allow it to multiply, and finally to encyst. The cysts 

 may then be picked up by means of a capillary pipette 

 and transferred to fresh culture medium, when one 

 is almost certain to obtain a practically pure mixed 

 culture. Further subcultures can be made by inocu- 

 lating the cysts into fresh dishes of hay-infusion, and 

 by this means the race may be kept going for months, 

 or even years. 



Even if the cultures dry up, and remain dr\' for a 

 month or two, it will still be found possible to obtain 

 a supply of organisms by scraping some of the brown 

 deposit from the inside of the dish and placing this 

 in fresh sterile hay infusion. After a few davs 

 amoebae will be plentiful, having hatched out of the 

 cysts contained in the deposit from the old culture. 

 ' Such a cyst-containing deposit or old culture con- 

 taining cysts can be kept as a stock, and when active 

 amoebae are required all that is necessary, is to seed 

 a dish or two of hay-infusion with cysts two or three 

 days before the organisms are wanted, and one can 

 be' certain of obtaining a good supply of active forms. 



I shall be pleased to supply anv zoological depart- 

 ment with a small quantity of cyst-containing deposit 

 or old culture liquid containing cysts of the form 

 cultivated here in case no success is obtained with 

 the method described above. T. fiooDEY. 



Department of Zoology, The University, 

 Birmingham, July i6. 



SCIENTIFIC PLANT BREEDING. 



SO much attention has been directed to the 

 purely scientific advance that has followed the 

 birth of Genetics as a new branch of science that 

 little reg-ard has been paid to the very remarkable 

 results already reached by the application of ^fen- 

 delian methods to the problems of economic plant 

 production. It is necessary to distingfuish some- 

 what sharply between the facts which Mendel was 

 the first to discover, and the hypotheses which 



