ACETIC ACID. 



[ 5 j 



ACHLYA. 



granules which are detached from the inner 

 surface of the pai'ent cyst. In the examination 

 of cysts supposed to be hydatids, careful 

 search should be made for the hooks of EcJii- 

 nococcus, which can frequently be found 

 when no fiuther remains of the body are di- 

 stinguishable. These hooks are figured in 

 PI. 16. fig. 1 b. See Entozoa and Echi- 



NOCOCCUS. 



ACETIC ACID. This is the weU-kno\Mi 

 acid of vinegar. 



It occm's in the juice of the flesh of ani- 

 mals ; sometimes in the stomach in indiges- 

 tion ; also in the human blood after the use of 

 alcoholic liquids, and in that of animals whose 

 food has been soaked in spuit. It is also a 

 common product of the decomposition of 

 vegetable substances, both by fermentation 

 and in thstillation, as well as a component of 

 the natural plants, mostly combined with 

 lime or potash ; it is also a rare constituent 

 of some mineral waters. 



The only salts of this acid requiring men- 

 tion, are the acetate of copper (neutral), 

 which is made by dissolving common verdi- 

 gris in excess of dilute acetic acid, filtering and 

 crystallizing upon the slides. The crystals, 

 when mounted in Canada balsam, exhibit 

 well the phaenomena of dichroism. PI. 31. 



Acetic acid is one of the most common 

 and valuable micro-chemical reagents. It 

 is particularly useful on account of its action 

 upon animal cells in general, rendering the 

 cell-walls transparent and the nuclei more 

 chstinct. The ordinary strong acid (sp. gr. 

 1048) should be used. 



ACHETA. — A genus of Orthopterous in- 

 sects, one species of which, A.domestica, the 

 house-cricket, is famihar to everyone. The 

 general stnicture of this insect agrees so 

 closely with that of Blatta orientalis, the 

 common cockroach or black beetle, which is 

 described at some length, that it requhes no 

 special notice here. (See Blatta.) Some 

 parts of the internal structm'e of the cricket 

 are verv beautiful, as the tongue (PI. 2Q. 

 fig. 23) and the gizzard (PI. 27. fig. 1). These, 

 as also the cm-ious mechanism by which the 

 chirping noise of the male is produced, are 

 described under Insects. 



ACHLYA, Nees (Soprolegnia, Kiitzing). 

 — A genus of Siphonese (Confervoidese). Re- 

 markable microscopic plants, here referred 

 to the Algae, but by some accounted as Fungi. 

 They are found gro\Aing parasitically upon 

 the bodies of dead flies hing in water, also 

 upon fish, fi'ogs, &c., and in some cases upon 



decaying plants. To the naked eye they ap- 

 pear like colom-less minutely filamentous 

 tufts adherent to such objects, forming a kind 

 of gelatinous cloud more or less enveloping 

 them. When placed beneath the microscope 

 the tufts are seen to consist of long, colour- 

 less, tubular filaments, spreading out in all 

 du'ections, with or without lateral branches ; 

 these erect filaments arise from a kind of my- 

 cehum of ramified filaments hang upon the 

 object upon which the plant grows. The 

 erect filaments are devoid of septa, nan'owed 

 upwards, and vary in thickness, being usually 

 of smallest diameter in those cases where 

 they are closely crowded ; the ordinary thick- 

 ness varies from 1-1000 to 1-350 of an inch. 

 The tubes contain a colourless, slightly gra- 

 nular protoplasm, which is denser on the 

 walls, and these sometimes exhibit an irre- 

 gular spiral arrangement of the granules; 

 the granules are seen to move slowly in ana- 

 stomosing currents running in various direc- 

 tions, exhibiting, that is, the well-knovATi 

 phaenomenon of the circulation of cell-con- 

 tents, such as is met with in the hairs of Tra- 

 descantia, &c. The walls of the tubes are 

 colom*ed blue by iodine and sulphm'ic acid, 

 therefore consist of cellulose ; the contents 

 are nitrogenous, taking a bright yellomsh 

 brown with iodine ; no trace of starch or of 

 chlorophyll can be detected in the cell-con- 

 tents in this stage, whence these plants are 

 regarded by some authors as Fungi ; but, as 

 mentioned hereafter, Pringsheim states that 

 their ripe spores do contain starch. 



Kiitzing describes a number of species of 

 this genus, under the name of Saprolegnia, 

 while a recent obsen^er, Pringsheim, regards 

 them all as forms produced by varying ex- 

 ternal conditions. The latest writer on this 

 subject, A. de Bary, separates Achlya proli- 

 fera, Nees, from Saprolegnia fer ax, Kiitzing, 

 referring to the former the Saprolegnia fe- 

 rax of Cams and the Saprolegnia capituli- 

 fera of Alex. Braun, to the latter the Achlya 

 prolifera of Cai-us, and, doubtfully, the S. 

 molluscorum of Nees and Gruithuisen. The 

 distinction between these hes in the details 

 of the formation and emission of the active 

 gonidia or zoospores. The following is a 

 description of the phaenomena as presented 

 by two of the forms : 



1. Achlya prolifera, Nees {Saprolegnia 

 capitulifera, Al. Braun). — In about thu-ty^-six 

 hours after the appearance of a specimen on 

 any body, the apices of the erect filaments 

 exhibit remarkable changes. The granular 

 protoplasm, which at first was equally dif- 



