476 Prof. A. B. Macallum. Detection and Localisation 



nucleoli of the nerve cells in the spinal cord of Menobranchus and of 

 the ox and dog, give a deep reaction, but it is not uniform through- 

 out the nucleolus, portions of a granular form, giving a deeper 

 colour than the surrounding material. 



In the cytoplasm of various cells the organic phosphorus present 

 is usually small in amount, and, unless inorganic phosphates are 

 present, the lecithin being extracted, the reaction is a very faint one. 

 In the cells of the nucellus and in the bast cells of Erythronium a 

 deeper reaction is obtainable in the cytoplasm ; and this appears to 

 be due to the presence of chromatin at least in the case of the 

 nucellar cells. The cytoplasm of the latter is also, as I have pointed 

 out elsewhere, iron-holding. Other exceptions are found in the 

 pancreatic cells, liver cells, nerve cells, striated muscle fibres, in 

 maturing and mature ovarian ova of Amphibia, and in the spermato- 

 zoids of Ascaris. These exceptions are referred to at greater length 

 below. 



In dividing cells the achromatic spindle gives no reaction for 

 phosphorus. This result is quite the opposite of that which Heine 

 obtained when he used stannous chloride as a reducing reagent after 

 the employment of the nitric-molybdate 'reagent. Heine advanced 

 the view that his result showed that the molybdic reagent could not 

 be depended on to indicate the presence of phosphorus in tissues. It 

 is rather to be interpreted as indicating that stannous chloride does 

 not distinguish between the molybdate and the phospho-molybdate 

 compounds. 



In no case has the centrosome or centrosphere in animal and 

 vegetable cells given a reaction for phosphorus. 



II. Special. The zymogen granules in the pancreas of Diemyctylus, 

 from which the lecithin was thoroughly extracted, gave a deep reac- 

 tion for phosphorus after eighteen hours' treatment with the nitric- 

 molybdic reagent. The phosphorus apparently is less firmly bound 

 than is the case in the nuclear chromatin in the same cells, for the 

 reaction in the latter is slower in appearing. A very distinct but 

 less deep reaction was obtained also in the protoplasm in which the 

 granules lie, more especially in the part adjacent to the lumen, and a 

 marked reaction also was produced in the antecedent substance of 

 the zymogen, found usually in the outer or protoplasmic zone of the 

 cells. This substance, which I have named prozymogen,* contains 

 iron in a " masked " form, and it stains in every way like chromatin. 

 The presence of phosphorus, as well as of " masked " iron, seems to 

 indicate very clearly that it is a nucleo-proteid. 



The demonstration that zymogen and prozymogen are pbosphorus- 



* Loc. cit., p. 224 ; also " Contributions to the Morphology and Physiology of 

 the Cell," ' Trans. Can. Inst.,' vol. 1, p. 247, 1891. 



