678 



lion will be, so lliat more serum is set free. Onlj v\itii veiT 

 strongly diluted latices a Hockj coagiiliim is separated, wliicli does 

 not form a coherent lump, or oulj gradually coheres after one or 

 more days. If we use less acid, the coagulation sets in slowly ; b<it 

 with decreasing quantity of acid the sjiontaneuus coagulation, caused 

 by bacteria which decompose the sugars and the |)roteins under 

 foiiuation of aciil, begins to play a more and more important part. 

 Ordinai'y, non-sterilised latex always coagulates, e\en without any 

 addition of acid, during the tirst night aftei' tapping; the coaguluni 

 is then spongy by the formation of gases, and the surface exposed 

 to the air is covered with a yellow, evil smelling layer of porridge- 

 like separated rubber, mixed with decomposition jtroducts of proteins. 

 So in the range of very little acid there are no n)ixtures, which 

 remain liquid in the long run; the observation "liquid" may be 

 made after a quarter of an hour or after (wo hours, but after 24 

 hours one will find the mixture coagulated. The li(iui(l nuxtures 

 with nacre acid, so in what one might call the second liquid range, 

 remain liquid for an unlimited space of time. Sometimes, after being 

 left to ihem3elve.s for several days, a separation of very thin little 

 tlocks, lying on an almost clear or whitish .serum, sets in, b\it in 

 any case one can control and confirm the observation "liquid" after 

 24 hours. This liquid range passes into the ranges of coagulation by 

 a strip of transition, being broad especially towards the side of the 

 higher acid concentrations, and distinctly showing different stages. 

 The first beginning of coagulation phenomena is the apj>earance of 

 a thin skin at the surface of the liquid, caused by evaporation in 

 the air, which, on stirring with a glass rod, attaches itself to it as 

 a streak or rolls itself u|). 



On approaching the range of coagulation a little more, this streak 

 becomes thicker and more cloddy. Advancing further, we get to 

 clotting or curdling of a greater part ot the latex; a pap and finally 

 a coherent coagulum is formed. If it is left longer to itself, the 

 coagulation in this range of transition proceeds further; what after 

 two hours was a pap, may after 24 hours ha\e become a coagulum 

 and a mixture which after two hours o\\]y showed a thick streak, 

 has changed the next morning into a pap, or even may be coagu- 

 lated. What is liquid in the middle of the second range, remains 

 liquid even after days, but "liquid" on the limit of "streaky", may 

 have changed into streaky after 24 hours. "Coagulated" of course 

 remains such after one or several days, only the coagulum gradually 

 contracts itself a little and becomes harder. 



It may be clear, that with these gradual transitions, we shall 



