64 PHYSIOLOGY OP NUTRITION. 



as to the growth capacity of the plants under the conditions de- 

 scribed. If we estimate the Nitrogen in the dry substance (best 

 by the well-known Kjeldahl method), we find among other things 

 that the peas grown in nitrate-free soil often contain large quan- 

 tities of Nitrogen, while the oat plants grown in nitrate-free soil 

 are at most only a few milligrammes richer in Nitrogen than the 

 seeds sown. 



The peas (and other Papilionaceee, e.g. lupins, beans, etc., 

 behave in a similar manner), as we may already conclude from 

 consideration of the results of these preliminary investigations, 

 are able, in absence of nitrates from the soil, to utilise elementary 

 Nitrogen for proteid formation. Oat plants and very many others 

 cannot do this. Our present experiments, it is true, do not settle 

 this latter point with absolute certainty ; but we must pass by 

 experiments which are thoroughly conclusive, 2 and proceed to in- 

 vestigate still further the behaviour of the Papilionaceas towards 

 elementary Nitrogen. 



A number of glass cylinders of the dimensions above given are 

 provided with quartz sand and food solutions, etc., but without 

 addition of Calcium nitrate. The vessels are first carefully 

 cleansed with sublimate-solution (1:1000), and then rinsed out 

 with alcohol. The quartz and cotton wool are heated to 150 C. 

 in the drying chamber before being introduced into the cylinders. 

 The sand, mixed with Calcium carbonate in the quantity already 

 specified, is heated in a large sand-bath for two to three hours to 

 about 180 C., and filled into the cylinders while still warm. We 

 now add to it the food solution, this having first been boiled for an 

 hour in a flask closed with cotton wool, and then after two days 

 for four hours in the steam steriliser * (to be obtained from H. 

 Rohrbeck, Berlin. See Catalogue, 1887, p. 9). The seeds, peas, 

 are first placed for two minutes in sublimate solution (1:1000), 

 then rinsed with boiled water, and sown in the sand. The surface 

 of the sand is covered with sterilised cotton wool. For watering 

 nothing but boiled distilled water is to be used. We weigh the 

 cylinders daily, and so determine the loss of water by evapora- 

 tion, and hence how much water must be supplied to the soil. 



One or more of the cylinders receive no further addition. To 

 others are added 25 c.c. of an extract of fertile garden or field 



* It might be better to put in the quartz and moist sand, mixed with food 

 stuffs and Calcium carbonate, and then cover the cylinders with glass plates, 

 and sterilise them in the steam of the steriliser. 



