21 



All these samples contain ammonia and nitrate, although the 

 amounts are low. Indeed, those from the Butt of Lewis and 

 Vifilsstadir are the lowest hitherto recorded, the amount of ammonia 

 in the Butt of Lewis rain being even less than was found in the 

 southern regions by the Charcot expedition. 



Seeing that ammonia is always present, it is important to ascer- 

 tain where it comes from. The old theory of Boussingault, that 

 atmospheric ammonia is derived from the sea, and the more recent 

 one of Schloessing, that tropical seas give up ammonia to the air, are 

 not supported by any analyses of rain collected near the sea in tropi- 

 cal countries, all of which show less ammonia than is found at 

 Rothamsted. The only possible explanation seems to be that the soil, 

 or at any rate arable soil, is continually giving up some of its 

 ammonia to the air. So that instead of the rain contributing three 

 or four pounds to the acre, it seems more probable that it is merely 

 restoring some portion of the ammonia which the soil has previously 

 lost. 



XI. "The Excystation of Colpoda Cucullus from its Resting 



Cysts, and the Nature and Properties of the Cyst 

 Membranes" T. GOODEY. Proceedings of the Roval 

 Society, 1913. 86 B, 427—439. 



This research has shown excystation is brought about in con- 

 sequence of the dissolution of the cyst membrane by an enzyme, and 

 an attempt has been made to follow out the main steps of the process. 



The cyst membranes of Colpoda cucullus consist of the outer 

 ectocyst and the inner endocyst, and the reactions of each have been 

 studied. The endocyst appears to be of carbohydrate nature, but it 

 differs from any other carbohydrate and appears to be new. The 

 name "Cystose" is suggested for it. During excystation the endocyst 

 is set free by the rupture of the etocyst, and the Colpoda liberates 

 itself by the rapid digestion of the endocyst by means of an enzyme 

 which it secretes. This enzyme differs from diastase and other 

 known enzymes, and is named Cystase. Full details are given in the 

 paper of the tests adopted and the results obtained. 



XII. "Soil Protozoa:' K. R. Lewin and C. H. Martin. 



Nature, 1914. 92, 632 (Feb. 5, 1914). 



A method of obtaining permanent preparations of protozoa in 

 the state in which they are living in the soil. 



The fixative hitherto used in our experiments has been picric 

 acid in saturated aqueous solution, but we have since found this re- 

 agent to be less serviceable in the case of clay soils than the 

 following mixture : — Saturated aqueous solution of mercuric chloride, 

 1 pt.; methylated spirit, 1 pt. The soil should be crumbled into 

 this fluid, and mixing is best accomplished by gently shaking the 

 containing vessel, care being taken to avoid making the clay com- 

 ponent of the soil pass into suspension. 



A delicate film containing protozoa appears on the surface 

 of the liquid, and this can be removed by floating cover-slips over it, 

 and stained by the usual methods. 



