R help - Jul 2012 - network plot problems

Hi,

I wanted to create a network of drugs that are being studied together.
So, I created a file as a graph.
But plot of my network is not corect!
It looks like to me that something else is lying behind this network links
created.

Could someone help me with this?

Thanx!

a<-read.graph(file=file.choose(), format="edgelist")
plot.igraph(a)

File (number present ID of drug):

15 2
10 4
10 4
10 4
13 4
13 4
15 4
18 4
11 5
2 6
7 6
7 6
7 6
12 6
15 6
15 6
19 6
22 6
24 6
6 7
5 12
5 12
7 12
11 12
13 12
13 12
13 12
13 12
16 12
17 12
23 12
23 12
23 12
23 12
6 13
12 13
6 14
6 15
9 15
12 15
13 15
17 16
16 17
1 18
12 18
23 18
2 19
6 19
24 19
21 22
3 25
5 26
6 27
7 27
15 29
20 30
25 31
28 31
8 32
6 33
14 33
22 34

-- 
**************************
Vlatka Matkovic Puljic
+32/ 485/ 453340

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