266 A C TINOMYCOSIS. 



and the colonies of the parasite can be seen lying in the 

 pus. Microscopically these abscesses show collections of 

 ordinary pus corpuscles, in which colonies of the parasite 

 lie, and which are enclosed by strands of granulation tissue. 

 Later the abscesses become confluent, and form large 

 areas of suppuration. The pus in these abscesses is 

 usually of greenish-yellow colour, and of somewhat slimy 

 character. 



In cattle the tissue reaction is more of a formative 

 type, there being abundant growth of granulation tissue 

 around the parasite, which may lead to the formation of 

 large tumour-like masses, usually of irregularly nodulated 

 character. The cells immediately around the colonies are 

 usually irregularly rounded, or may even be somewhat 

 columnar in shape, whilst farther out they become spindle- 

 shaped and concentrically arranged. It is not uncommon 

 to find leucocytes or granulation tissue invading the sub- 

 stance of the colonies, and portions of the parasite, etc., 

 may be contained within leucocytes or within small giant- 

 cells which are sometimes present. A similar invasion of 

 old colonies by leucocytes is sometimes seen in human 

 actinomycosis. The spread of the disease is usually more 

 rapid in the human subject, and this is associated with 

 abundant growth of the parasite in the filamentous form, 

 and with much suppuration. 



Origin and Distribution of Lesions, The lesions in the 

 human subject may occur in almost any part of the body, 

 the paths of entrance being very various. In many cases 

 the entrance takes place in the region of the mouth prob- 

 ably around a decayed tooth by the crypts of the tonsil, 

 or by some abrasion. There is reason for believing that 

 growth often takes place first in such situations, and after- 

 wards the parasite invades the tissues. Swelling and 

 suppuration may then follow in the vicinity, and the disease 

 may spread in various directions. It may attack the 

 periosteum of the jaw or the vertebrae, producing caries or 

 necrosis, or the pus may spread deeply in the tissues of the 

 neck, and may even pass into the mediastinum. Occasion- 



