HISTOLOGICAL DEMONSTRATIONS. 53 



produced by the protoplasm. It is not a deposit from the 

 surrounding fluid ; for it is known that the envelope of the 

 vegetable cell consists of cellulose, and there is certainly no 

 cellulose in Pasteur's fluid. 



c. Rupture the torulse. For this purpose make a pad 

 of blotting paper, place it on the cover-glass, and beat it 

 with the handle of a needle. Colourless ruptured envelopes 

 will then be found scattered throughout the field, while the 

 coloured protoplasm lies in masses here and there. Some- 

 times it is only partially outside the ruptured bag. 



65. PeniciUium.* (H.) Examine in water. Observe 

 that the hyphae (stems and rootlets) consist of chains of 

 elongated cells. Each aerial hypha (stem) produces at its 

 summit four or five rows of small germ-cells (conidid) of a 

 greenish colour. Even after staining with magenta no 

 nucleus is rendered visible in any of the cells. (This 

 fungus closely resembles the Achorion Schonleinii met with 

 in the hair follicles in Favus.) 



66. Starch. (H.) a. Gently scrape the cut surface of 

 a potato with a scalpel ; place the scraping on a slide ; add 

 a drop of water ; diffuse the scraping in the water with the 

 point of a needle ; remove all coarse particles ; apply the 

 cover-glass ; and examine the starch corpuscles. 



Observe their lines arranged concentrically around a 

 bright refracting spot the so-called " nucleus " of the cor- 

 puscle. This " nucleus " appears merely to be the first part 

 of the concretion that is produced, the various layers being 

 deposited concentrically around it. That the concretions 

 are produced within the protoplasm of the cell, may be readily 

 seen in a very thin section, with a power of about 800 diam. 



b. Allow a drop of iodine solution (tincture of iodine i 

 part, water 1 2 parts) to flow under cover-glass, and observe 

 the blue coloration of the starch. 



67. Cotton Fibres. (H.) a. Place a few fibres of 

 cotton wool on a slide in a drop of the above iodine solu- 

 tion ; cover, and examine. Notice the twist that is charac- 



* The green dust of common mould should be blown upon the 

 surface of modified Pasteur's fluid ten days or so beforehand. Fungi 

 grow rapidly in this fluid. 



